Paper 5 – Since When Is Arsenic Methylation A Bad Thing?

Arsenic can be found world-wide in drinking water. Humans and other organisms have well studied mechanisms to eliminate arsenic taken into the body from drinking water or other sources. Traditionally arsenic methylation has been considered part of the elimination process.

In the 2006 JBC paper “Human arsenic methyltransferase (AS3MT) pharmacogenetics: gene resequencing and functional genomics studies.” by
Wood TC, Salavagionne OE, Mukherjee B, Wang L, Klumpp AF, Thomae BA, Eckloff BW, Schaid DJ, Wieben ED, Weinshilboum RM.

We discussed a variant with 350% of the enzymatic activity compared to the wild-type protein, and a series of genetic variations in the 5′ UTR of the methyltrsnsferase gene.

So, how could an enzyme with improved activity be bad?

And, why would mutations in a part of the untranslated region of an mRNA effect the methyltransferase activity?


26 thoughts on “Paper 5 – Since When Is Arsenic Methylation A Bad Thing?

  1. This paper on arsenic methylation is incredibly hard to read and understand because it is filled with abbreviations and is written in intense scientific terms. I know for a fact that if I did not pay attention in class on Thursday that I would be completely lost, somewhat confused and would not know how to respond. So the paper is on attempting to improve our bodies’ natural ability at transforming arsenic into a safer form for excretion. There were several important aspects of this research that were discussed, certainly one of them being gene re-sequencing, because like other articles, this too must stay true to the nature of our course. In the article a team of scientists identified specific nucleotide changes in the useful part of our DNA and the corresponding amino acids changes. They used cell culture for enzymes with genetic variations in the 5’ UTR and compared it to the wild type.

    The result of their analysis suggested that a super enzyme, Thr287 has a extremely high enzymatic activity for methylating arsenic, roughly 350%. This is terrible, because it is going to produce too much methylated arsenic and can make certain people become sensitive to arsenic. In addition to this, mutations in the uncoding sequence of an mRNA can also cause similar overproduction of methylated arsenic. In either case, it would be a bad thing to allow excess methylated arsenic be present in the body.

    I found the discussion on using race to approve drugs, to be insufficient and a unsafe measure because we are not genetically proven to be who we think we are. Especially for those with parents of different races, how can we possibly place those individuals into a single category, when their genetic background is so diverse? And how can we be sure that individuals within the same race did not experience genetic mutations?

    Perhaps using race to approve drug is a closer step towards personalizing medicine, but just because personalizing medicine is harder than we expected, we should not just settle for an easy way out. We have the proper knowledge and the technology to make it happen and I think we should have faith in making that goal come true.

  2. In this paper, the methylation of arsenic is discussed. The human body uses a specific gene, the AS3MT gene, to detoxify arsenic in the human body. This was first discovered in a rat model with this gene. By using this gene, the arsenic has a methyl group added on it which actually makes it cytotoxic. Even though the arsenic is now in a more toxic state rather than broken into less toxic molecules, the body gets these molecules out of the body quicker because it is so toxic through sweating or other execratory processes. On this gene, polymorphisms were focused on to determine the effect that they have on methylation of arsenic.

    Most of these polymorphisms showed a smaller enzyme activity than produced by the wild type gene. This is in a way to be expected by the researchers. There was however one experimental polymorphism, the Thr287, showed a 350% enzyme activity. This polymorphism had improved activity from the wild type gene. This increase in activity would be seen as a good thing because it’s allowing the arsenic to be removed quickly from the body. This enzyme is more active, binds better and acts quicker in the body. It is actually worse for this enzyme activity to be so high. When this enzyme is working, it is producing high amounts of methylated arsenic, which is actually putting high amounts of a more toxic substance in the body. With this polymorphism in the gene and in this enzyme, it can explain why people can have a high sensitivity to arsenic.

    Also in this paper, it was stated how these polymorphisms are found in the untranslated regions of the mRNA. This goes to show that even mutations in the UTRs of the gene are just as important as those that are translated.

    Overall, I found this paper difficult to read on my own. I thought that there was a lot of scientific jargon in it and that unless you did research or had a lot of knowledge in the field, then you wouldn’t be able to comprehend it. After discussing it in class, the paper made a lot more sense to me. The use of so many abbreviations had something to do with why it was so hard to know what exactly they were talking about in the paper. I think that overall the topic of the paper was definitely interesting though since it is an interesting process that is done within the body and can explain arsenic sensitivity.

  3. Arsenic can cause many health problems in a human such as: cardiac failure, peripheral neuropathy, leukopenia, neurotoxicity, hepatic injury and carcinogens. This is a serious problem since Arsenic contaminates ground water worldwide, making methylation an important procedure in our body. The article Human Arsenic Methyltransferase Pharmacogenetics is trying to prove that over expression as well as low expression levels lead to Arsenic poisoning.
    In this paper they mention that the methylation of Arsenic is an important reaction in the process of detoxification of Arsenic from the body, but methylated Arsenic is more cytotoxic and genotoxic than arsenate, which is the most stable form of Arsenic. Also these methylated derivatives are potent inhibitors of glutathione, thioredoxin reductase and pyruvate dehydrogenase. These facts about methylated Arsenic is what lead scientist to believe it is more dangerous than unmethylated Arsenic. Thus this papers main focus is in the many allozymes responsible for methylation of Arsenic, so as to prove what happens with to much methylated Arsenic in the body and when methylation enzymes do not work properly.
    The article proved that the enzyme Thr 287 shows increased levels of enzyme activity, therefore producing to much methylated Arsenic. In contrast the enzymes Trp 173 and Ile 306 showed significantly decreased levels of enzyme activity. These results prove that if individuals with the Thr 287, which is 10% frequent in African Americans and Caucasian Americans, are exposed to Arsenic their bodies will over express it and create to much methylated Arsenic instead leading to increased risks for cytotoxic and genotoxic effects. In the other hand those who have Trp 173 and Ile 306 might not be able to methylate the Arsenic and die of Arsenic poisoning.
    Another point the article mentions is what happens when mutations occur in untranslated regions of mRNA, and what would be its effects. For me these mutations would cause the untranslated mRNA to become part of the coding mRNA which in turn would cause the synthesis of a totally different protein. These proteins are what then form the enzymes responsible for the methylation of Arsenic, therefore a mutation would disrupt the methylation.

  4. Human Arsenic Methyltransferase Pharmacogenomics addresses the variability in response to arsenic exposure in humans. It focuses on researchers can make the body’s response to this exposure more effective. The gene of interested located is AS3MT which was found in a model species (because testing on humans would be too risky) and shows that it is Aresenic Methyltransferase. the idea behind it is that the arsenic is metabolized so as to make it less toxic and easier for excretion. It was shown that arsenic molecules that have a methyl group attached to it kills the ells faster but if taken and distributed throught the body rids the body of the arsenic more quickly and therefore the organism would have less exposure to it.
    The problem with an enzyme with improved activity is that the enzyme itself is toxic. If someone is being treated with more of the enzyme the buildup of the enzyme puts them in greater danger than if they had simply been exposed to the aresenic, versus the arsenic and an additional toxin. Thr287 at a rate of 350%, would be the “super enzyme” that quickly methylates the aresnic but because it iself is toxin poses danger to a percentage of the population who are more sensitive to it due to inherit and unknown variabilities such as personal genetic backgrounds.
    It was also revealed that P\polymorphisms are found in untranslated regions of the mRNA which do not fall under the coding sequence. It is important as far as genetically influenced drug production because it is less assuring for researchers that a cultural based drug is effective. The paper was difficult to understand as an entry-level reader because it contained many words and abbreviations that made reading it confusing. The main point of the paper was that though a percentage of people in a population can be identified as more or less sensitive to aresenic exposure, UTR makes the process of personalized medicine more complicated.

  5. Arsenic is a danger threat to the human immune system; as it can commonly cause health problems. This is a widely growing issue as it seems that arsenic is found to be contaminating the undergroud water that supples us today.
    The paper on Human Arsenic Methyltransferase Pharmacogenomics discusses how the human body can and will react to arsenic exposure upon different levels. In the experiement explained in the article, scientists attempted to clone a rat gene to see if it was possible to resequence a humam gene between different races. During the human gene resequencing, they observed genetic polymorphisms and haplotypes in the human AS3MT gene which brought us a step closer in realizing that the experiment needed to be directed towards a more individual based variation on arsenic levels among humans. The polymorphisms found in RNA are important genetically speaking because they do not fall under the coding sequence which can lead to all sorts of other issues.
    It has been found that methylated arsenic is more harmful to the human body than unmethylated arsenic. This article discusses ways to act when the body’s natural methylation enzymes are not working properly, arsenic can be too stable to break down and excrete properly; leading to health issues such as neurotoxicity or cardiac failure. Arsenic methyltransferase needs to be metabolized to be made less toxic, but it has been shown to have a methyl group, which if the wrong enzyme is added to the mix, the body could be at a greater danger than if it were just intoxicated with arsenic alone.
    This paper was particularly difficult to respond to because the constant abbreviations and different explanations of complex enzymes. Overall, the paper was the most exciting to me out of the ones we have looked into this semester. I think it is a particularly intersting subject, and offers a lot of insight in our chosen feild of work.

  6. The paper article concerns an AS3MT, or human arsenic methyltransferase, an enzyme involved in the methylation and biotransformation of Arsenic. For centuries, there have been documented cased of human toxicity exposure to arsenic. Arsenic poisoning in humans usually occur from occupational exposure in smelting industries, pesticides and through ground water contamination. Arsenic is known to cause several toxic effect in humans some including carcinogenesis, neurotoxicity and hepatic injury. In the study, scientists set out to research the pharmacogenetics of human arsenic methyltransferase. There may be a possibility that the inherited variations in AS3MT may contribute to the variation in metabolism of arsenic, which may lead to more toxic effects. If genetically, a variation in this enzyme, some people may be more susceptible to arsenic toxicity. Scientists began the research by taking sixty samples from white Americans as well as black Americans. They then placed these genes in animals to test the enzyme.

    Improved enzyme activity in the case of AS3MT could be bad because the increase causes the arsenic to undergo biotransformation more rapidly, thereby eliminating it faster through the body, However, increase enzyme activity causes the arsenic to bind quicker to the body and cause more toxic effects. The high activity of this enzyme causes the arsenic to methylated quicker, and arsenic in the methylated form, is more toxic. If scientists could find that increased susceptibility to arsenic toxicity is cause by the rapid biotransformation caused by this enzyme, it would be a major achievement in the pharmacogenomics science. Mutations in the untranslated regions of mRNA effects this enzyme activity because if the mRNA has not yet been translated, it may be more susceptible to mutations. Untranslated mRNA can be affected due to the fact the its process is not yet complete.

  7. Arsenic can contaminate water worldwide and cause health problems such as cardiac failure, neuroxicity and carcinogenesis. Methylated Arsenic (AsIII), which is regarded as a detoxification reaction, is more cytotoxic and genotxic than arsenate and arsenite. This article talks about research done on arsenic methyltrasnsferase activity in rats to determine if AS3MT like other human methyltransferase genes include genetic polymorphisms that contribute to certain diseases or individual responses to arsenic therapeutic agents.

    Some enzymes such as Thr287 displays increased arsenic methylation levels of 350% compared to the other polymorphisms that showed a smaller percent of enzyme activity than the wild type. While this improved activity is removing arsenic quicker, it is not a good thing because it is also putting subjects at an increased risk for cytoxic and genotxic effects if exposed to arsenic.

    Polymorphisms are also found in the untranslated regions of mRNA. This is important because the untranslated regions that contain mutations could become part of the coding sequence and disrupt, change, or destroy the protein.

    This paper contains many topics of what we have been learning in class, and procedures we have done in lab which made it very interesting for me to read. I found it a little difficult to understand, but it became clearer to me after our discussion about it in class.

  8. Exposure to arsenic can have severe consequences which include carcinogenesis and neurotoxicity. Due to its toxicity, humans have a gene that allows them to methylate arsenic in order to get rid of it. Although methylated arsenic is secreted must faster, it is also much more toxic. The study in this paper takes a deep look at the enzyme that catalyzes the methylation of arsenic and how chronic exposure to arsenic can affect the gene for this protein, AS3MT.

    The paper looks at various mutations of the AS3MT gene which affect the activity of the enzyme that methylates arsenic. The wild type gene was found to have a 100% activity while three of the studied mutations had much lower percentages of activity. One mutation however, Thr287, was found to have 350% enzymatic activity. In the case of this paper, improved enzyme activity is bad because methylated arsenic is much more cytotoxic than unmethylated arsenic. So a gene with the Thr287 mutation will lead to over activity of this enzyme which will cause any exposure to arsenic to be methylated at a much higher rate and percentage. This could possibly lead to a fatally toxic level of arsenic in a person. This mutation causes a person’s body to be able to tolerate a much lower amount of arsenic.

    Mutations in a part of the untranslated region of an mRNA affect the methyltransferase activity because although these regions are not translated, they do contain regulatory sequences and protein binding sites necessary for mRNA translation. If there is a mutation in these UTRs, the regulatory sequences will be different and the protein binding sites will be altered which will ultimately affect how the mRNA is translated. This will lead to a mutated gene.

    This was a more difficult paper to read than the previous four. Despite its difficulty, it was interesting to learn how an untranslated region of mRNA can lead to a protein mutation. I also found it interesting to learn about a reaction that speeds up the breakdown of arsenic but at the same time makes it more toxic.

  9. “Human arsenic methyltransferase (AS3MT) pharmacogenetics: gene resequencing and functional genomics studies” addresses a rather interesting topic, interesting because it could potentially relate to each or every one of us. In general the paper addresses the issue of the carcinogen arsenic, although very useful in the treatment of leukemia it is also the causative agent of many complications, acute exposure alone can cause cardiac failure, leucopenia and even death. The purpose of the paper is to identify the relationship between arsenic methylation and specific polymorphisms. The polymorphisms experimented on were Trp173, Thr287 and lle306 which are all found on the AS3MT gene which is the gene used to cleanse arsenic from the body.

    Researchers found that Trp173 and lle306 displayed poor enzymatic activity compared to the wild type activity, however Thr287 had remarkable enzymatic activity, it showed roughly 350% activity compared to the wild type. This at first appeared to be a good thing since it allows for arsenic to be cleansed from the body in a swifter manner however this is not a good thing because it increases the level of toxicity inside of the body and therefore may be more harmful. Not only is that an issue but this could very well be the cause for the development of sensitivity to arsenic in organisms.

    An interesting part of our discussion was when we discussed approving drugs by means of race. It may not be the best choice to base such decisions off of compared to allele typing and other types of genetic testing but I do believe that it is the most sufficient at this moment other methods would just be too timely and costly. I believe that it is just a start and that the method we use to approve drugs will change as more methodology are developed but for now it is probably the most effective choice considering that people of the same race often show genetic similarities and are often from the same or similar populations.

    Another issue was the effect of mutations in a part of the untranslated region of an mRNA and how it would affect the methyltransferase activity. If this were the case it would alter the synthesis of protein, potentially destroying it. Overall this paper kept my interest but through it off at certain points because of the abbreviations and terminology, besides that the information discussed was well presented.

  10. Ambreen Yousuf

    When arsenic is exposed to the human body, it can result in cardiac failure, leucopenia, and sometimes can even lead to death. Over time arsenic has become an important environmental carcinogen that contaminates ground water all around the world. The paper has discussed the process of methylation which is a detoxification method of arsenate. By understanding how the enzyme catalyzes forms of arsenate can serve as an important step to understanding consequences of these exposures.

    The paper made an interesting observation which shows that as the level of enzymatic activity increases, the arsenic methylaiton also increases. This means a higher risk of toxicity and arsenic exposure. When arsenic is added to a methyl group, it makes it even more toxic, and kills a higher amount of cells. An enzyme temporarily binds to reactants in order to lower the activation energy and help speed up a reaction. Often times we would think this a good thing, since a superenzyme lasts longer and binds to the substrate better. However we quickly learn that these higher levels of enzyme activity can do a lot of damage. The higher the activity, the more methyl arsenate is created at a faster rate. As we have discovered, high levels of methyl arsenate can be dangerous to human health. Depending on the sensitivity of a person, intoxification can affect them at unusually high levels or normal levels.

    Mutations often occur in untranslated regions (UTR) of the mRNA. This is also where the VNTR region is which is known as a repeat sequence. If a mutation occurs in this region, this repeat sequence can further repeat again and again as shown in figure 3. If there is enough number of repeats, this can become common in the race type of a human. This can lead to further changes in how amino acids are encoded. Decreased levels of proteins that the amino acids encode for result in accelerated degradation of the variant allozyme. It is seen that the AS3MT has a VNTR sequence beginning at 5`, which can often influence transcription. For example, the shorter the repeat length in HepG2 cells, the more enhanced the reporter gene transcription. In conclusion, if the amino acids are altered in their structure, enzymatic activity could decrease in turn affecting methyltransferase activity.

    Though the topic of this paper was very interesting, its complicated terminology lost me many times. But overall i think it discussed an important matter of research which can help us to control exposure of certain chemicals asides from arsenic. Once we can understand this concept to its best, we can help avoid exposure to these chemicals and decrease the affects of its toxicity in humans.

  11. The contamination of groundwater by arsenic has become a high-profile problem in recent years due to its widespread and serious environmental effect. This predicament mainly affects populations who depend on groundwater for food preparation and beverages. Arsenic is a naturally occurring substance that can result in high levels of toxicity within humans and other organisms. However, there are various forms of arsenic that produce specific effects on humans that are based on sensitivity. This paper attempts to detect what the determinants within exposed human beings for sensitivity are for arsenic poisoning.

    Through the use of a rat model, scientists recognized that the body utilizes AS3MT as a detoxifying agent for arsenic. It was discovered that if they took arsenic and placed a methyl group on it then it would make it more cytotoxic. However, in a whole organism this same compound would be eliminated from the body more rapidly. It is stated in the paper that this increase in enzyme activity can be bad for the body. It is discovered that although methylation has been regarded as a detoxification reaction, methylated AsIII is more cytotoxic and genotoxic than are arsenate (the most stable form of arsenic) and arsenite. Methylated derivatives are also more potent inhibitors of glutathione reductase, thioredoxin reductase and
    pyruvate dehydrogenase than is arsenite.

    In this article, scientists also utilized Linkage disequilibrium mechanisms in order to determine the likely hood of a certain combination that would lead to dysfunction. Through linkage disequilibrium it attempts to set up a relationship that will predict the amount of things that goes through them. This technique can limit the number of experiments on what goes on between the cells during methylation. With the use of Polyclonal antibody, scientists can indicate an antibody through the coding sequence.

    The mutations of one part of the untranslated region of an mRNA can effect the methyltransferase activity. The researchers can make a super enzyme with one mutation or two bad enzymes with a bad mutation. When there is a bad mutation, then the enzyme will not remain in the system, will rapidly degrade and will not bind well. These mutations can give different amounts of transcipts, as well. In this article, the super enzyme is not better because it creates too much of a toxic form of arsenic. As a result, people who are really sensitive to arsenic create a pool of poisonous arsenic within the body. This article was very interesting, however it was difficult to read and understand.

  12. This paper discussed how sequence variation in AS3MT might contribute to individual variations
    in risk for arsenic toxicity.
    One surprising observations made in this experiment showed an increased levels of enzyme activity and
    protein for the common Thr287 allozyme when compared with WT AS3MT. Because the frequency of this polymorphism is
    expected to be homozygous for this allele, patients might have higher levels
    of AS3MT, and increased arsenic methylation. They also might be at increased risk for the cytoxic and genotoxic effects of arsenic exposure, since methylation
    enhances arsenic toxicity.

  13. Arsenic, a substance toxic to our body, can be found in the very water that we drink every day. Luckily, our body has a way of getting rid of the arsenic that comes onto our bodies by methylating the arsenic. This means that our body adds a methyl group to the arsenic. The reaction acts as a signal to our body that we need to get rid of it. However, the methylated arsenic is more cytotoxic and genotoxic to our body than arsenate, which is the most stable form of arsenic. The AS3MT gene is what is found to be responsible for this biotransformation or arsenic.
    According to this article, there are three known mutations: Trp173, Thr287 and Ile306. Thr287 mutation can be good and bad for our bodies. It works as a better methyltransferase compared to the wild type and the other two types of mutations. This means that more arsenic will be methylated. In addition, this mutation helps the methyltransferase bind very tightly to the substrate, and it lasts longer. On the other hand, Thr287 mutation will make a huge amount of methylized arsenic, creating a pool. If arsenic that is methylated is very cytotoxic, than if there was a pool of them, then it can be even more toxic to the body.
    If the mutations were part of the untranslated region of the mRNA, then the methyltransferase activity would be changed. The untranslated region in the mRNAcontains a lot of valuable information, such as instructions of where to start, how long the enzymes lasts, and how much of it to make. If there was a mutation to occur there, then that would mess up its original function, causing more or less methyltransferase activity.
    This paper was very hard to understand. It took me awhile to figure out what the tables was showing and how it corresponds to the results. I also had a hard time figuring out what this paper was trying to prove. I found that it was a bit more interesting once we discussed it in class.

  14. Arsenic is one of atoms that exists everywhere in the earth, therefore, it affects every day of human life. Either acute or chronic arsenic exposure brings significant diseases to human; however, on the other hand, people use it for therapeutic agent. In this paper, the researchers focused on the relationship of the enzyme that catalyzes the formation of methylated arsenic for the better knowledge of arsenic-dependent carcinogenesis.
    In this paper, it tested 5 different models of recombinant allozymes’ enzyme activity and immunoreactivity of proteins. They tested WT, Trp173, Thr287, Ile 306, and Thr287/Ile 306 models. Among those samples, especially, Thr287 showed high percentage of AS3MT allozyme enzyme activity and highest level of immunoreactive protein (however, Thr287/Ile306 was worst than WT.) It means this mutated enzyme binds arsenic tighter, lasts longer, and more stable, so it help to for methylated arsenic. Specially, human body gets rid of arsenic by forming methylated arsenic. So this super mutant looks helpful for discharging the arsenic, but it brings adverse effect that human body would be more sensitive for the arsenic. In the other words, when the sensitive body is exposed arsenic, the body cannot handle to detoxinate the metal. Since the methylated arsenic is cytotoxic and genotoxic, having the super mutant is not good.
    Mutations in a part of the untranslated region (UTR) of an mRNA affect the methyltransferase activity. UTR is the part that translating to protein. However, especially, mRNA’s 5’UTR has important role for forming translation initiation complex and recognizing start codon (AUG). So, if there were mutations in the UTR, the subsequence translation will be ruined.
    Personally, I was having confused time for reading this paper because there were many abbreviations and the multiple tests. I liked the class discussion because I got more concepts for this paper. Sicne peoeple are exposed arsenic in the nature, I hope scientists research more about the relationship between arsenic and human body so that people can live free from arsenic dependent carcinogen.

  15. I thought that this paper was mind boggling to read with so much scientific terms and technicality. The discussions in class about the paper helped simplify the understanding of the topic. The paper discusses about arsenic and the methylation in our bodies associated with it. Although many people think of arsenic as a dangerous toxin, it is used as an important environmental carcinogen that for contamination of ground water and is also a therapeutic agent for treatment of diseases one particularly common is for promyelocytic leukemia. Arsenic may contribute to the environment but arsenic exposure to our bodies can cause harm. Even minute amounts can cause cardiac failure, peripheral neuropathy, leukopenia, and death. The human body uses AS3MT gene which is a specific gene used to detoxify arsenic in our bodies. This was discovered through an experiment with a rat by cloning the cDNA encoded with the arsenic methyltransferase gene. Even though this AS3MT gene is a detoxifier, it is more cytotoxic and genotoxic than arsenate and arsenite which are supposedly the most stable form of arsenic. Even though the arsenic is more toxic, it is more readily removed as the body gets rid of these molecules and substances quicker due to being it more toxic through processes such as sweating.
    The AS3MT gene was focused on with polymorphisms to determine its effects on the body. Much of the polymorphisms showed much low activity in the enzyme than the wild type gene. One polymorphism had a staggering result of the Thr287 which showed 350% enzyme activity. This super enzyme activity is supposed to be good in the sense that the enzymes are working more quickly to get rid of the arsenic in the body, however it is actually harmful for this enzyme activity to be improved because it leaves unwanted high amounts of methylated arsenic in the body system. It was interesting to see that these polymorphisms are actually found in the untranslated region of an mRNA which goes to show how these untranslated genes might actually affect the human body in various ways and is subject for further studying. I thought that the experimentation of the paper was really difficult to understand and I honestly did not know how this experiment was going on even though it was explained in detail. I got the jist of the overall reasons and the resulting outcome of the studies. I thought it was interesting to see how a higher toxic molecule would be readily processed in the human body than its most stable form. It made me think of how complex the human body works and made me understand how improved enzyme activity can cause more harm than reduce it due to build up of unwanted toxins in the body.

  16. This paper is about the enzyme called arsenic methyltransferase and as it name suggests it is involved in then methylation of arsenic in humans. Arsenic is a very hazardous substance that if it somehow gets into a organism can be very lethal and can have very adverse effects on the expression of genes. Acute arsenic exposure can result in cardiac failure, peripheral neuropathy, leucopenia, and death, whereas chronic exposure can lead to neurotoxicity , hepatic injury, and carcinogenesis.

    In the experiment there are described several examples of the mutated AS3MT gene and the wild type of the gene. This gene effects enzyme activity of arsenic methylation. The reason for why this enzymes hyper activity is bad for us is that the enzyme methylizes arsenic at much higher rate than it could be removed from our body through its removal system. This Methylated arsenic is then more dangerous than ordinary arsenic. One more important fact about this paper is the mutation in untranslated regions of mRNA. This mutation of RNA is also important because of its impact in protein synthesis. A misfolded protein can either not perform its job in the methylation of arsenic. So we can conclude that any action in our body, that if it’s not balanced with the rest of the system its bad.

    These papers are very helpful in describing and explaining the work and impact of pharmacogenomics in modern medicine even when I read it for the 11th time because I always somehow wonder off when I start reading the sentences filled with scientific short terms. Anyway the discussion in class was extremely helpful and simplified it until the point that I can understand it and write something about it and not just writing a long essay that probably even I would not understand.

  17. An enzyme with improved activity, like Thr287, could possibly be bad because even though it shows increased levels of both enzyme activity and immunoreactive protein. This could be unfortunate because it could lead to increased risk of cytoxic and genotoxic effects from methylation enhancing arsenic activity.
    The methyltransferase activity of an mRNA would be effected by mutations in its untranslated region because “expression of reporter gene constructs for the 5-flanking region and the variable number of tandem repeats in the 5-untranslated region demonstrated cell line-dependent variation in reporter gene expression”. When a study was done with the HepG2 cells and HEK293 cells, certain sequences were joined with other particular sequences and there were specific instructions on how the gene was expressed in the untranslated region. If there were a mutation in the untranslated region which is the region with the regulatory genes of the reporter region, the activity in that region would not go as it normally would have tampering with the amount or way the product is formed.
    There should be further study on the alteration in sequence for a major arsenic-metabolizing enzyme in humans because it would contribute to the theory about how natural selection is taking place slowly and mutations are no longer considered abnormal. Degradation levels also led to no certain conclusions about the variant allozymes because they observed no “significant alterations” in degradation for them.
    This paper was difficult to understand but I am glad that in class we go over every concept separately and it is our job to connect it in these papers. I still feel like I don’t understand what I write (completely) but all of the papers are beginning to connect to each other and I can refer to the past papers to make sense of the recent ones.

  18. This enzyme (Thr278) with improved activity just works too well. Its ability to methylate so well creates a worse, more toxic, arsenic that can be more harmful to the cell and organism as a whole.
    The non-coding protions of mRNA dictate the life span and function of the molecule as a whole; even though the mutation is found in an untranslated portion of mRNA and doesn’t get encoded into protein, the mutation can indicate how, when, or where the protein will be created. In my opinion, the mutant mRNA that codes for Thr278 is worse than a mutant proetin derrived from a mis-transcribed mRNA.

  19. Arsenic exposure can result in cardiac failure, peripheral neuropathy, leucopenia, and death, whereas chronic exposure can lead to neurotoxicity and carcinogenesis. Since methylation is an important reaction in the biotransformation of arsenic, AS3MT plays a vital role in humans to detoxify the arsenic. An arsenic methyltransferase activity was recently described in the rat that catalyzes the methylation of arsenic, with S-adenosyl-L-methionine as a methyl donor. In rats, that activity is expressed in a variety of organs, and a similar activity is expressed in the human liver, kidney, and brain. Therefore, this research article scrutinizes the gene AS3MT while considering the enzymatic activity and catalysis of methylation of arsenic. Also, it looks at different mutations of the AS3MT gene which affect the activity of enzyme and methylates arsenic.

    Usually arsenic contains a methyl group which makes it cytotoxic and in humans methylated group in arsenic breaks down and disoriented from the body which makes it more toxic/poisonous. The researchers found that wild type gene contained 100% and Thr287 resulted in 350% enzymatic activity. Thr287 works more efficiently than wild type and also methylates arsenic at high rate which is not good for human body. And since arsenic levels determine the methylation, it also controls the mechanism and extent to which it can lead to various diseases and thus human body has high sensitivity to arsenic.
    Mutations in a part of untranslated region of an mRNA affect the methyltransferase activity because the part of UTR also contains some proteins which have the ability to transcribe mRNA. Sometimes, the front end of untranslated region binds to reporter region which affects transcription and results in a mutated mRNA.

    I enjoyed reading this paper because it reveals important research about arsenic and how it methylates to result in a cytotoxic substance and harms human body in different ways. But I had a difficult time reading and comprehending this article due to its use of scientific words and was able to completely understand after class discussion.

  20. Arsenic is a metal that has been found to be a source of contamination in water. Humans are also exposed to arsenic in smelting industries and through pesticides. Humans, fortunately, can use the process of methylation to transform arsenic. The process of arsenic methylation is very important because arsenic is a toxic element that can lead to many health problems such as cardiac failure, carcinogenesis, hepatic injuries, and neurotoxicity. This paper focuses on the pharmacogenomics of the process of arsenic methylation in humans specifically the AS3MT gene, which encodes for this process. This gene contains three polymorphisms, which are Trp173, Thr287, and IIe306. Thr287 had 350% more enzymatic activity and was shown to be more harmful to humans because it increased the toxic levels in the body. The higher enzymatic activity leads to higher rates of arsenic methylation. But this also consequently means a greater concentration of methylated arsenic in the body, which is harmful to the body because it leads to cytotoxic effects. So this enzyme has an improved activity but the greater concentration of the product leads to adverse effects in the body proving to in fact be a bad mutation and showing how overexpression can be fatal. The other two mutations, Trp173 and IIe306 express less enzymatic activity, which leads to less arsenic being methylated and this leads to arsenic poisoning. Mutations in a part of the untranslated region of an mRNA would affect the methyltransferase activity of the gene because the regulatory sequences in this region will affect the translation of the gene and thus its activity.

  21. Methylation is known as a detoxification reaction, which helps the body produce methylated arsenic metabolites. Some are even used to treat patients with promyelocytic leukemia by working as a therapeutic agent. Therefore, methylated arsenic derivatives can be recognized as working to function with improved activity as a result of faster biological metabolism. But contrary to popular belief, methylation of arsenic such as AsIII, is more cytotoxic and genotoxic, that is, it is more potent physically and genetically with the risk of being potentially mutagenic and cancerous than are arsenate and arsenite. With this in mind, the function of the enzyme that catalyzes the formation of methylated arsenicals is crucial for understanding variations in effects to humans and the biological consequences of exposure to arsenic as well as possible variation in the gene that contributes to encoding proteins with that activity. In this case, an enzyme with improved activity can be bad because it promotes much faster cytotoxic action by increasing the degree to which an agent can possess the quality of being toxic to cells. Apparently, AS3Mt, the gene that contributes to the subsequent encoding of protein that expresses arsenic methylation, or better known as arsenic methyltransferase, is characterized by a series of genetic polymorphisms and haplotypes. These polymorphisms which occur in a part of the untranslated region of an mRNA can affect the methyltransferase activity because they express elevated levels of AS3MT, and perhaps, even increased arsenic methylation. A two-way experimental test was performed to test the genotype and phenotype of AS3MT. The primary step included annotating the AS3MT gene, then resequencing of AS3MT took place for 60 DNA samples from AA (African American) and 60 DNA samples from CA (Caucasian American) subjects with their legal consent. The observations showed 26 single individual nucleotide polymorphisms (SNPs) and 3 nonsynonymous cSNPs as well as variable number of tandem repeats (VNTRs) in exon 1 within the cDNA 5′ -untranslated region. Variant allozymes of AS3MT and WT were then expressed using functional genomic studies of a mammalian expression system. Surprisingly, there were striking differences in levels of enzyme activity and immunoreactive protein among these allozymes, but one variant, which is the Thr287, demonstrated increased levels of both enzyme activity and immunoreactive protein when compared with the WT AS3MT. In addition, proteins encoded by genes containing nonsynonymous cSNPs express patterns of altered enzyme activity and protein similar to the variant allozymes of AS3MT. Therefore, subjects of both AA and CA would be expected to be homozygous for this allele or having two identical alleles for this gene (e.g. AS3MT), and are expected to be at risk of increased arsenic methylation due to elevated levels of AS3MT. As a result, high cytotoxicity and genotoxicity would be administered if, methylation of arsenic enhances toxicity.

  22. This paper discusses how methylation of a gene,AS3MT. Normally methylation causes the body to recognize the substance as a toxin and remove it more quickly, however in this particular case it causes the arsenic to be more cytotoxic to the body. So therefore the enzyme with sepd up activity actually is worse for the body. As far as Mrna is concerned: mutations in any portion of the gene replication can cause issues furthur down the line. In particular it affects the methyl transferase activity.

    I thought the idea of using race as a classification to approve drugs was absurd. RACE is NOT a genetic qaulifcation for anything. I am SPANISH CAUCASION- however when I am tan in the summer people may consider me HISPANIC. The two are very different things and I am only one.

    This paper was challanging and very heavy in technical jargon- perhaps the most yet. Overall interesting concept but I wish I didnt have to read it 5 times to understand

  23. Methylation, the process of replacing hydrogen(s) with methyl group(s), is an important part of the biostransformation of arsenic. Arsenic itself is a very harmful environmental carcinogen, cancer causing agent, that contaminates ground water world wide but in some forms it can be advantageous to use in the medical field for treatment on cancer treatments, ironically enough.
    The authors use the example of the gene AS3MT and its association with the methylation of arsenic as an example of how an improved enzyme actitivy can have adverse results on a person. With the help of encoded catalysts, there would be a greater amount of methylated arsenic in the body, therefore drastically increasing the amount of harmful carcinogens in the body, no matter how quickly they may be excreted out of the body. More is not necessarily better in some cases. There are more problems to consider even after the actual genetic encoding of such enzymes as well. While the genetic information may not be the source of the problem, there are many other ways in which methyltransferase activity can be affected such as misfolding,etc.
    Although it took a while for me to actually “translate” all the information from this paper into a valid repsonse, it was very insightful and maybe I can even use this information in the medical field later on.

  24. Arsenic exposure can lead to severe complications, the worst being death. Methylation is thought to be a detoxification reaction, but methylated Arsenic is more toxic to the body and genes than are arsenate. Methyltransferase has been described in rats and has helped our study of methyltransferase in humans.
    Two enzymes 173 and Ile 306 show a decrease in enzyme activity, people who have these enzymes might not be able to methylate arsenic causing them to get arsenic poisoning is exposed to too much of it. There is however an enzyme that has a 350% rate for methylating arsenic, and this is the Thr287 enzyme. This “super enzyme” causes the body to have levels of arsenic that are too high and can end up giving people a hypersensitive reaction to arsenic and can give your body a greater chance of getting genotoxic and cytogenic effects.
    One can find polymorphisms in the untranslated regions of mRNA. If these regions contain mutations they could through translation become a part of the coding sequence which could ultimately cause serious problem with or destroy the protein.

  25. Arsenic is an organic/inorganic compound that is currently contaminating our ground water everywhere. There are many forms of Arsenic and also it can be found in many forms such as Pesticides, Herbicides, and even Insecticides. The main exposure to Arsenic is occupational, mostly from smelting. The compound Arsenic is most commonly absorbed by the GI and dermal and excreted from urine.
    Human begins usually respond well to the compound Arsenic, where some will show no sign of intoxication and others will show high signs of toxicity in their system from arsenic. Currently scientists don’t understand the mechanism for people to develop cancer and the same hold true for arsenic poisoning. With this one question comes to mind, what are the determinants of sensibility? In this paper the scientists give us step by step experimental procedures on how they came to evolve the mechanism of getting rid of arsenic in ones system. First step was they determined which gene in the rat that would make it possible to resequence the human gene using DNA from two different “ethnic” groups. This gene was the Cyt19-As3mt. Then they proceeded to take the gene because it has been found that arsenic methyltransferase activity was illustrated in a rat that catalyzes the methylation of arsenite. The methyl group makes the arsenic molecule die quicker therefore proceeding to get eliminated faster than regular arsenic, killing the cells better and as a result there is less exposure overtime and with this method it evolves the mechanism of getting rid of arsenic.
    In biotransformation, methylation of inorganic arsenic which creates methylarsonic acid and dimethylarsinic acid is very significant because this allows us to see if the enzyme contains any polymorphisms that may be a contributing factor for arsenic poisoning. After they located the gene they began to resequence the AS3MT gene. With the sequencing of the gene they had to mark down every difference. Then they labeled the Variable nucleotide repeats (VNTR) which are repeated sequences where polymerase are polymerizing and can slide backwards and repeat a repeat during cell division. Next they found the variability which was found all over the gene. This can be seen in table 2 the VNTR. They then needed to identify the variability that they are able to see in the population. There can be two ways to identify this. One is that you can give the subjects the arsenic and see what the immediate result is or you can find a way to do it in a cell culture and see what the outcome is and this has proven to be the more efficient and effective method. One other observation that arose was that the increased levels of the enzyme activity and the protein THR287 , with this we can infer that these create high levels of toxicity for arsenic resulting in humans having a high sensitivity to arsenic. When mutations occur in the untranslated region of an mRNA would affect the methyltransferase activity because these mutations may find its way to become part of the sequencing process and therefore may cause disorder or may even destroy the protein.
    Overall this paper wasn’t that hard for me to dissect because I am currently taking principles in Toxicology and I have had some background on the Arsenic and its mechanisms. The only thing that may have been a bit hard to comprehend were the experimental procedures that they used, but when explained in class I was able to grasp the main concepts of the article.

  26. Arsenic is a natural mineral that has fatal effects on the human body. Ground water worldwide has some degree of arsenic contamination but thankfully our bodies have a way of detoxifying arsenic. Methylation is a process that involves the biotransformation of arsenic. Minimal arsenic exposure can result in cardiac failure, peripheral neuropathy, leukopenia, and death, but chronic exposure can lead to neurotoxicity, hepatic injury, and immediate cancer.

    The human body contains a gene that allows it to methylate arsenic but this comes with a negative effect. The AS3MT protein is released after a certain about of arsenic is detected in the body, it acts as a detoxifying agent for arsenic. Since methylated arsenic is secreted at a much faster rate and is much more toxic to the body it serves as a greater danger. After the methylated arsenic gets produced the AS3MT protein gets mutated this affects the activity of how fast the enzyme that methylates arsenic works. Three wild type gene were tested to see the activity rate before and were found to have a 100% activity while three of the genes after the mutations had much lower percentages of activity. The mutations can either increase or lower the rate. One specific mutation Thr287, increased enzymatic activity to 350%. But, increased enzyme activity is a false positive in this case because methylated arsenic is much more toxic than unmethylated arsenic. So a gene with the Thr287 mutation will lead to increased activity of this enzyme which will cause any exposure to arsenic to be methylated at a much higher rate and percentage and will kill the person at a faster rate than arsenic would originally.

    This paper was actually the most interesting paper out of the last four. The topics discussed in this paper are actually understandable and can be used as personal knowledge somewhere else. I enjoyed reading this paper.

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