Factors affecting peptide catabolism by oral streptococci.

The binding of a number of unsubstituted peptides to Streptococcus sanguis and Streptococcus mutans and their subsequent degradation by such cells were examined. Peptides were added to cell suspensions prepared from glucose-limited growth in a chemostat and, at appropriate time intervals, cell-free filtrates were analyzed for peptides and their constituent amino acid residues by high-pressure liquid chromatography techniques. The results indicated that peptide hydrophobicity plays a limited role in peptide binding, but that charge and chain-length are probably important. In S. sanguis, carboxypeptidase activity rapidly released C-terminal arginine (Arg); this amino acid was less rapidly released from the N-terminus but a number of other residues were also released by aminopeptidase activity. When Arg is buried in the peptide, the rate of its release depends upon the number and type of residues between it and the N-terminus. In contrast, S. mutans possessed only weak peptidase activities. The nature of its peptidase activities indicates that S. sanguis can obtain the metabolically important Arg from a variety of peptides.