[en] Evidence is given for the existence of at least four types of peptide cross-linkages in lysine-containing peptidoglycans of cell walls from Gram-positive bacteria. Three kinds of such cross-linkages, by which the є-amino group of the lysine residue of one peptide subunit is joined to the carboxyl group of the terminal D-alanine of a second, have been demonstrated, namely: bridging by tri-L-alanine (Micrococcus roseus Thr(-)), by tri-L-alanine-L-threonine (M. roseus R 27), and by pentaglycine (Staphylococcus aureus Copenhagen) residues. The lytic Streptomyces SA endopeptidase hydrolyzes D-alanylglycyl linkages in S. aureus and D-alanyl-L-alanine linkages in M. roseus, i.e., at the amino terminus of the peptide bridges and at the carboxyl terminus of the peptide subunits. The lytic Streptomyces MR endopeptidase hydrolyzes L-alanyl-L-threonine linkages within the peptide bridges in M. roseus R 27 and, with a much smaller rate, L-alanyl-L-alanine linkages within the peptide bridges in M. roseus Thr(-)). A fourth kind of cross-linkage, in which no additional amino acid is involved, can also occur in the form of a direct bonding between the C-terminal alanine residue of one peptide subunit and the є-amino group of the lysine residue of a second (Micrococcus lysodeikticus). This latter alanyl-є-lysine bond is sensitive to a third lytic Streptomyces enzyme, the ML endopeptidase. A structure for the peptide moiety of the peptidoglycan of M. roseus is proposed and compared to the peptidoglycan structure in S. aureus. The present studies lend support to recent proposals dealing with the mechanism of action of penicillin.
