The enzymic formation of hydrogen sulphide by certain heterotrophic bacteria. II

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Abstract
H2S formation from cysteine and from thiosulphate by Proteus vulgaris is due to the activity of 2 mechanisms in the cells. Its formation from organic S compounds by P. vulgaris and Serratia marcescens is due to activity of a highly specific enzyme in their cells. Sterile, cell-free solutions of this enzyme were prepared from P. vulgaris cells; as it exists in intact cells, it is inactive at pH 5.5, is most active at 7.8-9.0, and retains some 20% of its opt. activity at pH 12. It has an opt. temp. of about 40[degree], and is inactive at 50[degree]. The velocity of H2S formation is greatest under aerobic conditions. Non-viable, toluene treated bacteria retain over 50% of their opt. activity with respect to H2S formation. The reaction is only partially inhibited by cyanide (reversibly) and by ethylurethane; phenylurethane has no effect.

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