Abstract
Aminopeptidases from Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus were isolated. Enzymes were purified by chromatography on DEAE-cellulose and Sephadex G-150. The enzymes had molecular weights of 98,000 and 89,000 and optimal activity at pH 6.0 and 40°C and pH 6.5 and 35°C. respectively. The L. delbrueckii ssp. bulgaricus enzyme had higher activity on L-lysyl-4-nitroanilide than did the S. thermophilus enzyme. Both enzymes were inactivated by EDTA and 1,10-phenanthroline. Classical sulfhydryl and serine group reagents had little or no inhibitory effect on the enzymes; nevertheless, Cu++ and Hg++ resulted in strong inhibition; Ca++ stimulated the L. delbrueckii ssp. bulgaricus enzyme, and Mg++ stimulated the S. thermophilus enzyme.
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