Biosynthesis of the Peptidoglycan of Bacterial Cell Walls

The mechanism of addition of glycine during synthesis of the peptidoglycan of cell walls of Staphylococcus aureus has been investigated. Glycine was activated as glycyl soluble ribonucleic acid (sRNA) for this reaction. The initial acceptor for glycine was disaccharide(-pentapeptide)-P-P-phospholipid, an intermediate in peptidoglycan synthesis. Acetylmuramyl(-pentapeptide)-P-P-phospholipid also acted as a glycine acceptor, but less effectively. The glycyl-sRNA of S. aureus has been fractionated into two glycyl-sRNAs, only one of which was active in peptidoglycan synthesis. The product of this sequence, disaccharide(-pentapeptide-pentaglycine)-P-P-phospholipid, then transferred disaccharide-decapeptide to an endogenous cell wall acceptor. Analyses of the lipid intermediate and of the peptidoglycan product indicated that a chain of about 5 glycine residues was substituted on the e-amino group of lysine both in the lipid intermediate and in the peptidoglycan. These pentaglycine chains had free amino ends, and the closure of the pentaglycine bridges was therefore not catalyzed by the enzyme preparations employed. The inhibition of this system by various solvents, detergents, and antibiotics is reported. Two antibiotics, ristocetin and vancomycin, were specific inhibitors of the reaction sequence. Of the three reactions involved in the sequence (attachment of disaccharide-pentapeptide to the lipid, transfer of glycine to the lipid intermediates, and utilization of the lipid intermediates for peptidoglycan synthesis), the first was the least sensitive and the last was the most sensitive to these agents.