Anadi N. Chatterjee

[82] Membrane associated reactions involved in bacterial cell wall mucopeptide synthesis

Publisher Summary This chapter discusses the membrane associated reactions involved in bacterial cell wall mucopeptide synthesis. The particles catalyze the transfer of phospho-NAc-muramyl pentapeptide from uridine diphosphate (UDP)-NAc-muramyl pentapeptide to a phospholipid acceptor present in the particles with the release of uridine monophosphate (UMP). The reaction is assayed by measuring the incorporation of radioactivity into the particles or into the phospholipid or by an exchange reaction to detect the incorporation of radioactive UMP into UDP-NAc-muramyl pentapeptide. For the exchange assay, a quantity of UMP-H approximately equivalent in concentration and counts per minute to the UDP-NAc-muramyl pentapeptide is added to the incubation mixture. UDP-NAc-muramyl pentapeptide is the preferred substrate for the initial transfer reaction. UDP-NAc tripeptide is utilized at less than 7% of the rate of UDP-NAc-muramylpentapeptide. Glycine is accepted by any phospholipid-P-P-NAc-muramyl peptide which has lysine with an epsilon amino group free to accept it. It is not known whether glycine residues are added one at a time or as a peptide to form the tetra or penta glyeine units attached to lysine.

Regulation of the Bacterial Cell Wall: Effect of Antibiotics on Lipid Biosynthesis

Antibiotics that inhibit the biosynthesis of the cell wall, such as vancomycin, penicillin, d-cycloserine, and bacitracin, stimulate the incorporation of lysine into lipids that are extractable with n-butanol-6 M pyridinium acetate. Approximately 93% of this lysine is in lysylphosphatidylglycerol (LPG). The remaining lysine is incorporated in another as yet uncharacterized lipid. Because the lysine in the latter lipid is released by mild alkaline hydrolysis, it is not the C55-isoprenyl-pyrophospho-N-acetyl-muramyl pentapeptide. Vancomycin and penicillin stimulate the incorporation of lysine into both LPG and the minor lipid fractions, whereas treatment with d-cycloserine results in an increase only in LPG. Antibiotics that inhibit protein synthesis do not influence the incorporation of lysine into the lipid fractions. Analysis of the extracted lipids indicate that the incorporation of radioactive lysine into LPG is due to an enhancement in synthesis of LPG from phospholipids in the cytoplasmic membrane.