Abstract
Saccharomyces cerevisiae strains defective in cysteine biosynthesis were more sensitive to chromate than their corresponding isogenic prototrophic strains. Chromate sensitivity of the cysteine-dependent strains was reduced when L-cysteine was added to the growth medium. The effect of L-cysteine on chromate sensitivity was, however, not specific to the cysteine-dependent strains but was general to all strains tested. That is, addition of L-cysteine to the growth medium containing chromate caused an increase of colony-forming ability of chromate-sensitive, normal and chromate-resistant strains. It was also shown that L-cysteine nonbiologically consumed chromate. From these results, we conclude that cysteine plays an essential role in defence of cells against chromate. We contend that cysteine chemically reduces toxic hexavalent chromium to less toxic trivalent chromium; detoxication of chromate by this mechanism takes place intracellularly as well as extracellularly.
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