[Peptide hydrolases of lactobacilli of the Thermobacterium group. I. Demonstration of these activities in Lactobacillus helveticus, L. acidophilus, L. lactis and L. bulgaricus].

The intracellular peptide hydrolase activities of Lactobacillus helveticus, L. acidophilus, L. lactis, and L. bulgaricus were determined using various aminopeptidase, dipeptidase, and carboxypeptidase substrates in addition to casein and whey protein fractions. The different activities were then separated using disc gel electrophoresis. Each bacterium had aminopeptidase activity towards various amino acid beta-naphthylamides and dipeptides. The four species also showed bands of true dipeptidase activities on a large number of dipeptides. Intracellular enzymes from thermophilic lactobacilli also hydrolysed the whey proteins (alpha-lactalbumin and beta-lactoglobulin). From the results of electrophoresis on beta-casein and alpha s1-casein it was shown that beta-casein was totally hydrolysed by L. lactis while it was only partially hydrolysed by the intracellular enzymes of L. acidophilus and L. bulgaricus. On the other hand, alpha s1-casein was only partially hydrolysed by L. helveticus, L. lactis, and L. bulgaricus.