Peptidases of Lactobacillus casei and L. plantarum

Fractionation of cell-free extracts of Lactobacillus casei NCDO 151 (grown in Man's et al. (1960) broth) by polyacrylamide disc electrophoresis showed the presence of 4 constitutive peptidases. The enzymes appear to be a tripeptidase with a narrow substrate specificity, two true dipeptidases with identical broad-specificity, and a probable carboxypeptidase with broad-specificity. A probable amino peptidase could also be isolated from the cell-free extract by density gradient electrofocusing. Growth of the organism in skim milk resulted in the formation of two inducible dipeptidases. Examination of 5 other strains of L. casei for the presence of the two constitutive dipeptidases and the carboxypeptidase confirmed the results obtained for the species. Some strains, however, had one more peptidase. The peptidases of the strains differed relatively in the activity and substrate specificity from strain to strain. On polyacrylamide gel, the peptidase activity of L. plantarum appeared as one band only, probably of a carboxypeptidase.