Divalent mercaptans

The biochemical basis for the toxicity of mercury and mercury compounds results from its ability to form covalent bonds readily with sulfur. Prior to reaction with sulfur, however, the mercury must be metabolized to the divalent cation. When the sulfur is in the form of a sulfhydryl (— SH) group, divalent mercury replaces the hydrogen atom to form mercaptides, X—Hg— SR and Hg(SR)2, where X is an electronegative radical and R is protein (36). Sulfhydryl compounds are called mercaptans because of their ability to capture mercury. Even in low concentrations divalent mercury is capable of inactivating sulfhydryl enzymes and thus causes interference with cellular metaboHsm and function (31—34). Mercury also combines with other ligands of physiological importance such as phosphoryl, carboxyl, amide, and amine groups. It is unclear whether these latter interactions contribute to its toxicity (31,36). 

Bader H, Wilkes AB, Jean DH. 1970. The effect of hudroxylamine, mercaptans, divalent metals and chelators on (Na+ + K+)-ATPase. Biochim Biophys Acta 198 583-593. 

Thioalcohols, general formula R—SH, are the sulfur analogs of alcohols. Sulfur is below oxygen in the Periodic Table. Both are divalent and there are similarities in their behavior. Thioalcohols are also referred to as mercaptans. The SH group is referred to as the thiol or mercaptan or sulfhydryl group. 

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