PROTEOLYSIS BY LACTOBACILLUS CASEI II. PEPTIDASE AcIvrry1

A study of the proteinase activity of Lactobacil-lus casei grown in milk and of cell-free extract of L. cawi has been reported on in a previous paper (Brandsaeter and Nelson, 1956). Whereas the proteinases of L. casei have been studied to some extent earlier, very little has been done to characterize the peptidases of this organism. Other lactobacilli hydrolyze some peptides (Christophersen and Thiele, 1953, and Berger et al. 1938a). A survey by Berger et ca. (1938a), as well as more recent work (van der Zant and Nelson, 1954, Zimmerman, 1950 and Dudani, 1950), indicates that most peptidases produced by members of the family Lactobacteriaceae have maximum activity between pH 7.0 and pH 8.5. Metal activation of bacterial peptidases has been reported by several workers (Berger et al., 1938b, Dudani, 1950, Zimmerman, 1950 and van der Zant and Nelson, 1954). Manganese and magnesium and in some instances cobalt are most effective activators of peptidases. In the present work the characteristics of the peptidases of L. casei have been studied. Special emphasis has been placed on the effect of metallic ions on the activity of these peptidases. EXPERIMENTAL METHODS The preparation of cell-free extract of L. ca8ei strain 25 was carried out as described in a previous paper (Brandsaeter and Nelson, 1956). Activity of the cell-free extracts was tested on M/30 glycylglycine, diglycylglycine, glycyl-L-leucine, glycyl-L-tyrosine, glycyl-i-tryptophan and carbobenzoxyglycyl-L-phenylalanine, m/15 glycyl-DL-alanine, DL-alanylglycine, DL-alanyl-glycylglycine, DL-leucylglycine and DL-leucylgly