Biosynthesis of the Peptidoglycan of Bacterial Cell Walls

Abstract

Evidence has been obtained that the biosynthesis of a peptidoglycan with particulate enzyme from Staphylococcus aureus or Micrococcus lysodeikticus proceeds by a cyclic mechanism involving two lipid intermediates, as follows (the abbreviation Mur stands for muramyl). UDP-MurNAc-pentapeptide + P-phospholipid ⇄ UMP + MurNAc(-pentapeptide)-P-P-phospholipid (1) UDP-GIc-NAc + MurNAc(-pentapeptide)-P-P-phospholipid ⇄ GlcNAc-MurNAc(-pentapeptide)-P-P-phospholipid + UDP (2) GlcNac-MurNAc(-pentapeptide)-P-P-phospholipid + acceptor → GlcNAc-MurNAc(-pentapeptide)-acceptor + P-phospholipid + Pi (3) P-P-phospholipid is assumed to be an intermediate in Reaction 3. Both MurNAc(-pentapeptide)-P-P-phospholipid and Glc-NAc-MurNAc(-pentapeptide)-P-P-phospholipid have been obtained bound to the enzymes, and shown to be intermediates in the reaction cycle. Both of these intermediates have also been isolated from reaction mixtures with particulate enzyme from either organism by n-butyl alcohol extraction followed by purification on diethylaminoethyl cellulose and silicic acid columns. Analyses of GlcNAc-Mur-NAc(-pentapeptide)-P-P-phospholipid from both organisms are presented. Both MurNAc(-pentapeptide)-P-P-phospholipid and Glc-NAc-MurNAc(-pentapeptide)-P-P-phospholipid, isolated with the use of enzyme from M. lysodeikticus, were utilized for peptidoglycan synthesis by the particulate enzyme from this organism. Ristocetin and vancomycin at low concentrations inhibited utilization of GlcNAc-MurNAc(-pentapeptide)-P-P-phospholipid for peptidoglycan synthesis, thus confirming that this reaction is the step in peptidoglycan synthesis which is most sensitive to these antibiotics.