SUMMARY: Purified streptolysin-O, from group-C streptococci, H46A, whose identity with NAD-glycohydrolase (EC. was reported earlier, has been shown to hydrolyse 4-nitrophenyl-esters. With 4-nitrophenylacetate as substrate, K was 6.6 × 10 M; turnover number was 10000 mol substrate/mol enzyme/min and optimum pH was 7.8 to 8.5. Esterase activity was activated by SH-compounds and inhibited by diisopropylphosphofluoridate, mercuric salts and oxidizing agents. The effects of these agents on esterase activity were similar to their effects on the haemolytic activity of streptolysin-O protein so that both catalytic processes may be accomplished by the same active site.


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