Arsenic and other toxic metals and metalloids are known to have been dumped at numerous superfund sites. Two important biological mechanisms for detoxifying metal ions are protein binding, and methylating them via enzymes such as methyl transferases which use S- adenosylmethionine and/or vitamin B12 as coenzymes. This appears to be true for arsenic, selenium and possibly lead. The molecular mechanisms by which methylations are accomplished are unknown. The enzyme reactions for the biotransformation of arsenate/arsenite are unknown. Enzyme reactions for the biotransformation of arsenate/arsenite to the less toxic methylarsonate and much less toxic dimethylarsinate have been studied only to a limited extent using crude, impure enzyme homogenates of bacteria, fungi or the rat. There have also been limited, in vivo, metabolic studies in experimental animals and humans in which arsenic compounds were given and the metabolites in the urine identified. This project deals with the isolation and purification of human enzymes and binding proteins that detoxify arsenate/arsenite in order to study the molecular mechanisms of these detoxifications. In this way, for the first time, the enzymatic mechanisms for the detoxification of arsenate/arsenite in humans will be understood. Once the arsenic biotransforming enzymes have been characterized, other metal ions such as lead, selenium, cadmium, as well as, halogenated aromatic hydrocarbons will be studied to see if they inhibit the enzymatic biotransformation of arsenic. The control and regulation of these purified enzymes will be studied and inhibitors and stimulators of the enzymes will be studied. Urine of animals challenged with arsenate will be tested for methyltransferase activities to determine whether these enzymes can be used as biological indicators of the body's concentration of toxicologically active forms of arsenic. A challenge test for arsenic in humans using DMPS (2,3- dimercaptopropane-1-sulfonic acid) will be developed. Such a challenge test will be helpful for determining the exposure of humans to arsenic and will be useful to determine arsenic exposure of humans near superfund sites.

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University of Arizona
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