Biosynthesis of the Peptidoglycan of Bacterial Cell Walls

Abstract

Abstract A particulate enzyme system from strains of Escherichia coli is described which catalyzes the utilization of the uridine nucleotides, UDP-N-acetylmuramyl-l-Ala d-Glu-α, e-diaminopimelyl-d-Ala-d-Ala and UDP-N-acetylglucosamine, for peptidoglycan synthesis. Unlike the systems previously studied in gram-positive cocci, this particulate enzyme catalyzes the terminal cross-linking reaction in cell wall synthesis, a transpeptidation in which a d-alanine residue is lost from the end of one of the N-acetylmuramyl-pentapeptide residues incorporated into the product. The d-alanine residue is also lost from the end of the second unit involved in the cross-linking, apparently through the action of a d-alanine carboxypeptidase. Both the transpeptidase and the d-alanine carboxypeptidase are inhibited by various penicillins and cephalosporins.