A COMPARATIVE-STUDY - AMINOPEPTIDASE ACTIVITIES FROM LACTOBACILLUS-DELBRUECKII SSP BULGARICUS AND STREPTOCOCCUS-THERMOPHILUS

Aminopeptidases from Lactobacillus delbrueckii ssp. bulgaricus and Str eptococcus thermophilus were isolated. Enzymes were purified by chroma tography on DEAE-cellulose and Sephadex G-150. The enzymes had molecul ar weights of 98,000 and 89,000 and optimal activity at pH 6.0 and 40- degrees-C and pH 6.5 and 35-degrees-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 re agents had little or no inhibitory effect on the enzymes; nevertheless , Cu++ and Hg++ resulted in strong inhibition; Ca++ stimulated the L d elbrueckii ssp. bulgaricus enzyme, and Mg++ stimulated the S. thermoph ilus enzyme.