STUDIES ON AEROBIC DECOMPOSITION OF CYSTEINE BY ESCOHERICHIA COLI. I

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1. Cysteine was decomposed by living cells as well as by dried cells of E. coll. Hydrogen sulfide and ammonia were detected as the products.
2. The optimum pH of the reaction was about 7.
3. Initial velocity of the reaction was proportional to the amount of cells added.
4. Under the conditions used in the experiments, the rate of hydrogen sulfide production from cysteine by E. coli was independent of the cysteine concentration. The curve of hydrogen sulfide liberation was in good agreement with the theoretical one, calculated by assuming a stepwise reaction mechanism.
5. The cysteine decomposing reaction by E. coli occured only in the presence of oxygen or nitrate. The reaction was strongly inhibited by hydrogen cyanide.
6. Liberation of hydrogen sulfide from cysteine was preceded by cysteine disappearance and by detachment of amino group from cysteine.
7. When arsenite was added to the reaction mixture, there occured ammonia production without liberation of hydrogen sulfide.
8. In the presence of arsenite, a thiol keto acid was obtained from the reaction mixture. This substance was shown to be most probably thiolpyruvic acid.
9. The difference between the reaction and the corresponding reaction brought about by the action of cysteine desulfhydrase was discussed.