Effect of pH on mutagenesis by thiols in Salmonella typhimurium TA102.

The mutagenicity of thiol (SH)-containing compounds was tested in Salmonella typhimurium TA102 in the liquid preincubation method. Cysteinyl-glycine (CG), cysteine ethyl ester (CEE), L- and D-penicillamine (PA), cysteine (Cys) and glutathione (GSH) were mutagenic to strain TA102 without metabolic activation. On a molar basis, CG was the most potent mutagen. The mutagenicity of the remaining compounds decreased in the order specified above. The mutagenic response of each thiol-containing compound was a function of the pKa of the thiol group and the pH of the preincubation mixture. This indicates that a thiolate anion, rather than a free thiol, is required for mutagenesis.