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.