Peptidase and esterase activities from mutant strains of Lactobacillus casei

Cell‐free extracts from four Lactose‐negative strains of Lactobacillus casei and their parents were evaluated for peptidase and esterase activity. The four strains showed aminopeptidase (AP), dipeptidase (DP), carboxypeptidase (CP), aryl‐peptidyl amidase (APA) and caseinolytic activities. Very little differences can be noticed between the AP and DP levels of the different strains. On the other hand there were significantly higher CP activities in the Lac(+) strains 64H and ATCC 4646 when compared to the Lac(‐) derivatives. A difference in activity between the Lac(+) and its Lac(‐) derivative was also observed for the APA and caseinolytic activities. Parent and mutant strains of Lactobacillus casei posessed three active AP bands, with RF values of 0.18, 0.21 and 0.31 and one DP band with RF value of 0.25. An additional band (0.32) was detected in strain Lactobacillus casei ATCC 4646 Lac(+) and its mutant. As a general rule the rate of hydrolysis of the p‐nitrophenyl esters of fatty acids for the parent and mutant strains of Lactobacillus casei was higer than that of the o‐nitrophenyl derivatives. All the strains tested exhibited an esterase band with an RF value of 0.3, while only one substrate was hydroysed by the band showing a lower RF value. α‐Naphthyl butyrate was the only substrate hydrolysed by this enzyme in the case of Lactobacillus casei 64H and 11578 while it was α‐naphthyl acetate for ATCC 4646.