Michel Desmazeaud

Cell-wall-associated proteinases in Lactobacillus casei and Lactobacillus plantarum

Information concerning cell-wall associated proteinases of lactobacilli is limited. In Lactobacillus casei and Lactobacillus plantarum , presence of such proteinase is clearly shown. Differences between several strains were noticed. Higher cell-wall-associated proteinase activity can be measured in extracts obtained from milk-grown cells when compared to MRS-grown cells. No aminopeptidase, dipeptidase or carboxypeptidase activities were detected in the cell-wall-associated proteinase fraction. Isoelectric focusing of αs1-casein hydrolysates obtained by the action of this fraction from L. casei grown in milk revealed the presence of a major hydrolysis product and three minor degradation products with isoelectric points more acidic than αS1. Beta-casein was also degraded by the cell-wall extract with formation of one major product and several minor products with isoelectric points more acidic than β-casein. Two major hydrolysis products with isoelectric points higher than β-casein were also detected. Isoelectric focusing of αs1- and β-casein hydrolysates obtained by the action of the intracellular extracts of L. casei grown either in milk or in MRS broth shown identical patterns. As with L. casei , two strains of L. plantarum exhibited cell-wall proteinase activity. Milk-grown cells were more proteolytic than MRS-grown cells. Generally L. plantarum was significantly less proteolytic than L. casei .

The intracellular peptide-hydrolases of Lactobacillus plantarum. Comparison with Lactobacillus casei

Summary Although Lactobacillus plant arum has been isolated in large numbers from ripenedcheeses, the knowledge of its proteolytic system is very limited. This study was undertaken with the aim of obtaining a clearer picture of the peptide hydrolases of sorne L. plantarum strains. A comparison with the closely related species L. casei was also considered. The intracellular peptide hydrolase system of L. plantarum consists of aminopeptidase and dipeptidase activities in addition to a general activity on whole casein and ~-lactoglobulin. The electrophoretic pattern showed that it possesses one non-specifie aminopeptidase and three dipeptidases. By comparison L. casei aminopeptidase was very similar. This latter bacterium showed only one dipeptidase. Intraceliular extracts of L. plantarum are able to hydrolyse aSIand ~-casein. The formation of two peptides of higher mobility than casein was detected. It should be noticed that although similarities were found between the different strains of a sorne species on the type of enzyme, significant differences in the level of specifie activities were detected. In opposite to L. casei, L. plantarum does not possess carboxypepti