Proteinase enzyme system of lactic streptococci. 3. Substrate specificity of Streptococcus lactis intracellular proteinase

Proteolytic systems in lactic acid bacteria

The proteolytic systems of lactic acid bacteria are important as a means of making protein and peptide N available for growth and as part of the curing or maturation processes which give foods their characteristic rheological and organoleptic properties. The proteolytic systems of lactic acid bacteria are described in relation to their growth and their functions in protein-rich foods. Their role in the manufacture of milk products is discussed.

Fractionation of dipeptidase activities of Streptococcus lactis and dipeptidase specificity of some lactic acid bacteria

Proteins in sonic extracts of Streptococcus lactis were separated by starch-gel electrophoresis at high voltage. Each slab was sliced longitudinally, and half was stained for peptidases in a mixture containing a peptide, L-amino acid oxidase (snake venom), peroxidase, and o-dianisdine; the other half was stained in amido black for protein. In addition to sonic treatment, trypsin also released enzyme from acetone-treated cells. Glycyl-L-phenylalanine, L-phenylalanyl-glycine, L-alanyl-L-phenylalanine, and L-phenylalanyl-L-alanine served as substrates in characterizing the enzymes. Five different fractions of various specificities appeared in the gels. Broad-range substrate specificities were found for sonic extracts of S. lactis, S. cremoris, S. durans, and Lactobacillus acidophilus.

Hydrolysis of α s, 1 -Casein B by Streptococcus lactis Membrane Proteinase

The membrane-associated proteinase of Streptococcus lactis strain 3 hydrolyzed α s, 1 -casein B into 11 peptide fragments. Eight of the 11 peptides were purified and partially characterized. Each peptide contained several, but not all six, essential amino acids required for growth. The culture was able to utilize one peptide as the sole source for the essential amino acid leucine. Leucine, serine, valine, and glycine were found to be NH 2 -terminal residues. Two of the peptides were phosphopeptides. The data support the functional role of the membrane-associated proteinase as being involved in the initial breakdown of proteins to peptides.