Penicillin-sensitive Transpeptidation during Peptidoglycan Biosynthesis in Cell-free Preparations from Bacillus megaterium

The effect of penicillins and cephalosporins on the various transpeptidation reactions presented in the preceding paper is discussed. Inhibition by cloxacillin and penicillin G of [14C]diaminopimelic acid incorporation during peptidoglycan synthesis appeared to be partially reversible after the antibiotic was destroyed by treatment with penicillinase. Inhibition of the cross-linking reaction by cloxacillin appeared to be fully reversible. These and other results suggested the presence of more than one transpeptidase. In addition, a d-alanine carboxypeptidase activity present in the particulate enzyme preparation was examined and found to be irreversibly inhibited by penicillin G and relatively insensitive to cloxacillin. It is suggested that the transpeptidases(s) and the d-alanine carboxypeptidase are separate enzymes.