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Related Experiment Videos

Elucidating the pathway for arsenic methylation.

David J Thomas1, Stephen B Waters, Miroslav Styblo

  • 1Pharmacokinetics Branch, Experimental Toxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA. thomas.david@epa.gov

Toxicology and Applied Pharmacology
|July 28, 2004
PubMed
Summary

Researchers identified a novel S-adenosylmethionine (AdoMet)-dependent methyltransferase, named cyt19, in rat liver cytosol. This enzyme is crucial for the biomethylation of inorganic arsenic, a significant public health concern due to contaminated drinking water.

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Area of Science:

  • Biochemistry
  • Toxicology
  • Environmental Health

Background:

  • Arsenic biomethylation is critical for understanding its metabolism and toxicity.
  • Chronic exposure to inorganic arsenic in drinking water poses a global public health risk.
  • The precise molecular mechanisms of arsenic methylation in humans are still being elucidated.

Purpose of the Study:

  • To identify and characterize the enzyme responsible for inorganic arsenic methylation in mammalian systems.
  • To elucidate the molecular pathway of arsenic metabolism, converting inorganic arsenic to methylated forms.
  • To investigate the role of S-adenosylmethionine (AdoMet) in arsenic methylation.

Main Methods:

  • Purification and characterization of a novel methyltransferase from rat liver cytosol.

Related Experiment Videos

  • Enzymatic assays to determine the catalytic activity of the purified protein on arsenite.
  • Sequence analysis and comparison with known methyltransferases and cyt19 genes in mammalian genomes.
  • Studies with recombinant rat cyt19 protein to confirm its role in arsenic methylation.

    • Main Results:

    • A 42-kDa S-adenosylmethionine (AdoMet)-dependent methyltransferase, designated cyt19, was identified in rat liver cytosol.
    • Rat liver cyt19 catalyzes the conversion of arsenite to monomethylated and dimethylated arsenicals.
    • The protein shares sequence motifs with other methyltransferases and is homologous to previously uncharacterized cyt19 proteins in mouse and human.
    • Recombinant rat cyt19, with a reductant, can catalyze the complete methylation pathway from arsenite to methylated metabolites.
    • A proposed scheme links cyt19 and the thioredoxin system in arsenic methylation and reduction.

    Conclusions:

    • Cyt19 is identified as a key enzyme in the biomethylation of inorganic arsenic in mammals.
    • The findings suggest that cyt19 orthologs in humans and mice likely play a similar role in arsenic metabolism.
    • This discovery provides crucial insights into arsenic detoxification pathways and has significant public health implications for managing arsenic toxicity.