Comparative peptide specificity of cell wall, membrane and intracellular peptidases of group N streptococci

Abstract

Solubilized cell walls of group N streptococci contain 2 electrophoretically distinct peptidases, one of which hydrolzyed trileucine only, while the second hydrolyzed a wide range of di- and tripeptides. Neither enzyme possessed leucine aminopeptidase or endopeptidase activity. Four and 3 peptidases, respectively, were separated in intracellular extracts of Streptococcus lactis ssp. lactis and S. lactis ssp. cremoris produced by osmotic lysis of spheroplasts. In contrast with the cell-wall extracts, 2 of the peptidases had broad specificities, though only one of these hydrolyzed trileucine. Purified membranes of S. lactis ssp. lactis contained only 1 electrophoretically distinct peptidase of very narrow specificity. There were small differences between the numbers of peptides hydrolyzed by cell wall preparations from milk-growth or broth-grown cells.