Simultaneous deletion of D-alanine carboxypeptidase IB-C and penicillin-binding component IV in a mutant of Escherichia coli K12.

Mutants of Escherichia coli with much decreased activity of D-alanine carboxypeptidase (peptidyl-D alanine hydrolase, EC 3.4.12.11) were found among E. coli K12 extensively mutagenized with nitrosoguanidine treatment by assaying individual colonies for the enzyme activity. One such mutant with only 10-12% residual activity was characterized extensively. The soluble carboxypeptidase activity (corresponding to D-alanine carboxypeptidase IC of Tamura T., Imae, Y. & Strominger, J.L. [(1976) J. Biol. Chem. 251, 414-423] was deleted. This enzyme activity in the particulate fraction was markedly reduced but transpeptidase activity was normal. However, penicillin-binding component IV was deleted from the particulate fraction. Both the physiology and penicillin sensitivity of the organism were relatively normal, except that mutant cells were markedly more stable to penicillin-induced lysis, suggesting the possibility that carboxypeptidase IC really functions as an endopeptidase. The possible relationship of the deleted carboxypeptidase activity and the deleted penicillin binding component are discussed.