PURIFICATION AND CHARACTERIZATION OF AN X-PROLYL DIPEPTIDYL AMINOPEPTIDASE FROM LACTOBACILLUS-DELBRUECKII SSP BULGARICUS LBU-147

An X-prolyl dipeptidyl aminopeptidase that hydrolyzed L-glycyl-L-prolyl-p-nitroanilide was purified from cells of Lactobacillus delbrueckii ssp. bulgaricus LBU-147 and characterized. The purified enzyme was homogeneous in electrophoresis analysis and appeared to be a trimer because the molecular weight was 270,000 by gel filtration and 90,000 by SDS-PAGE. The optimal pH and temperature for activity were 6.5 and 50-degrees-C, respectively. The enzyme was strongly inhibited by metal ions and chemical reagents such as Hg2+, Cu2+, Fe3+ Fe2+, diisopropyl fluorophosphate, and p-chloromercuribenzoic acid, but it was weakly activated by sulfhydryl-group protective reagents such as 2-mercaptoethanol, dithiothreitol, and cysteine. These results indicated that this enzyme is a serine protease having its active site near a sulfhydryl group.