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

Abstract A particulate enzyme system from Bacillus megaterium QMB1551 is described which catalyzes the utilization of the uridine nucleotides, UDP-N-acetylmuramyl-l-Ala-d-Glumeso-Dap-d-Ala-d-Ala and UDP-N-acetylglucosamine, for peptidoglycan synthesis. Unlike systems previously studied in gram-positive microorganisms, this particulate enzyme preparation catalyzed the terminal cross-linking reaction in cell wall biosynthesis. This system could also incorporate free diaminopimelic acid dependent on the formation of peptidoglycan polymer from the uridine nucleotide substrates but independent of ATP. Furthermore, the incorporation of diaminopimelic acid was inhibited by penicillins, and the diaminopimelic acid appeared to be incorporated onto a terminal position of the peptide of a disaccharide-pentapeptide peptidoglycan unit with the release of alanine. The disaccharide-peptide products formed during the incorporation of free diaminopimelic acid were isolated from peptidoglycan and analyzed. A reaction sequence for incorporation of free diaminopimelic acid into peptidoglycan is proposed.