Arsenic biotransformations: The cycle of arsenic methylation and demethylation

摘要

Arsenic is the most prevalent environmental toxic element and causes health problems throughout the world. Here we will describe the connection between arsenic geochemistry and biology, with emphasis on redox and methylation cycles, as well as other arsenic biotransformations. The arsenic methylation cycle remodels the environment, with some members of microbial communities converting inorganic arsenic into organic species, and others breaking down organic arsenicals such as the arsenical herbicide monosodium methylarsenate (MSMA) into inorganic arsenic. The microbes, genes and proteins that carry out these pathways were identified. The enzymes were characterized, and their crystal structure solved. A new enzymatic mechanism for arsenic methylation by human AS3MT that accounts for the production of carcinogenic species is proposed.