| Abstract: | Nocardia asteroides was grown in Sauton medium containing sodium carboxy-14C]acetate. The biosynthesis of the peptidoglycan was inhibited by adding penicillin or phosphonomycin to the growth medium. These antibiotics give an accumulation of radioactive nucleotidic precursors of the peptidoglycan. In the presence of penicillin, there was an accumulation of uridine diphosphate-N-glycolylmuramyl peptide (UDP-MurNGlyc peptide) and of a mixture of uridine diphosphate-N-acetyl and N-glycolylmuramic acid (UDP-MurNAc) and UDP-MurNGlyc). In the presence of phosphonomycin, the biosynthesis of muramic acid was blocked and there was an accumulation of uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc) and uridine diphosphate-N-glycolyglucosamine (UDP-GlcNGlyc). Thus the formation of a N-glycolyl group can be performed upon the neucleotidic derivatives of glucosamine and muramic acid. However in the peptidoglycan synthesized in vivo in the absence of antibiotic, only muramic acid was glycolyated. So, glycolylation seems to take place essentially on UDP-MurNAc. When the binding of peptide chain to muramic acid is achieved, all the muramic acid is glycolylated, then the polymerisation of glycan and peptidoglycan units by the mean of particulate enzymes is carried out on the N-glycolylated derivative of muramic acid. A cell-free preparation from Nocardia asteroides was obtained which can hydroxylate the acetyl group of UDP-MurNAc. The activity was localised in the soluble fraction. This system acts as a hydroxylase and requires the presence of NADPH. |
