AMINOPEPTIDASE AND DIPEPTIDYL PEPTIDASE ACTIVITY OF LACTOBACILLUS SPP. AND NONSTARTER LACTIC-ACID BACTERIA (NSLAB) ISOLATED FROM CHEDDAR CHEESE

The complexity of the peptidolytic enzyme systems of a variety (67 str ains) of non-lactococcal dairy lactic acid bacteria was established. D iagnostic substrate hydrolysis by cell lysates confirmed the widesprea d occurrence of general aminopeptidase and dipeptidyl peptidase activi ties; lower levels of other more specific aminopeptidases were also in dicated. Inhibitor studies demonstrated that more than one type of leu cyl aminopeptidase and dipeptidyl peptidase were present in cell lysat es. Although both activities were susceptible to metallo- and serine-t ype inhibitors, the predominant aminopeptidase activity was associated with the metalloenzyme group whereas the principal dipeptidyl peptida se activity was mediated by serine-type protease action. Some characte ristics of individual enzymes comprising the aminopeptidase and dipept idyl peptidase activity were determined for components separated by po lyacrylamide gel electrophoresis and located in situ in the gel by act ivity staining with amidomethylcoumarin substrates. Three individual a minopeptidases with apparent molecular masses of 95, 44 and 30 kDa and a multimer (greater than or equal to 180 kDa) were detected. The 95 k Da and 44 kDa enzymes were metalloenzymes whereas the 30 kDa enzyme wa s a serine peptidase. The 95 kDa component thus resembled pepN while t he 44 and 30 kDa enzymes exhibited some characteristics of an infreque ntly described LAB metallodipeptidase and serine prolyl aminopeptidase , respectively. Two serine dipeptidyl peptidases, with apparent molecu lar masses of 88 and 125 kDa, were also detected after PAGE. The 88 kD a enzyme resembled X-prolyl-dipeptidyl aminopeptidase (pepX); the 125 kDa enzyme, not previously characterized in LAB, occurred widely among bacteria fi om this group. The lactobacilli, and other dairy lactic a cid bacteria examined, have a complex of enzymes involved in peptide t urnover, several enzymes of which have a commonality within the group. (C) 1998 Elsevier Science Ltd. All rights reserved.