Biosynthesis of the Peptidoglycan of Bacterial Cell Walls

Abstract The peptidoglycan of Staphylococcus epidermidis contains serine and glycine in the interpeptide bridges. A particulate enzyme system has been obtained which catalyzes peptidoglycan synthesis from the uridine nucleotides substrates and a transfer RNA (tRNA)-dependent incorporation of both serine and glycine into the peptidoglycan. Maximum serine incorporation requires simultaneous incorporation of glycine, but glycine incorporation is independent of serine incorporation. Serine and glycine are first activated, attached to tRNA, and then transferred to a lipid intermediate of peptidoglycan synthesis. Finally, this lipid intermediate is utilized in the biosynthesis of the peptidoglycan. The seryl-tRNAs of this organism have been separated into four seryl-tRNA fractions. Three of these function both in peptidoglycan synthesis and in protein synthesis, as examined by various methods. The fourth seryl-tRNA participates equally well in peptidoglycan synthesis, but it has not been possible to demonstrate its participation in protein synthesis or in triplet-dependent binding of aminoacyl-tRNA to ribosomes by using triplets corresponding to all of the known serine codons.