Journal of General Microbiology (rg77), 99,171-181 Printed in Great Britain Biosynthesis of Peptidoglycan in Wall plus Membrane Preparations from Micrococcus Zuteus: Direction of Chain Extension, Length of Chains and Effect of Penicillin on Cross-linking

A wall +membrane preparation from Micrococcus Zuteus was used to synthesize radioactively labelled peptidoglycan. The newly synthesized peptidoglycan either was cross-linked by transpeptidation to existing wall or remained associated with the membrane fraction but was not cross-linked. The average biosynthetic chain lengths, calculated from the ratio of free reducing groups of muramic acid to total muramic acid, were 66 disaccharide units for cross-linked and 26 disaccharide units for the uncross-linked material. The latter value was confirmed by the release of lactyl peptide side chains by p-elimination. Benzylpenicillin ( I pug ml-l) inhibited cross-linking but not overall synthesis of glycan whereas at concentrations above 10 pg ml-l overall glycan synthesis was slightly inhibited. In the presence of IOO pg benzylpenicillin ml-l the incorporation of disaccharide units to existing walls decreased to 25 % of the control. This residual incorporation represented extension by transglycosylation of peptidoglycan already cross-linked to existing walls. Chains with an average length of between 30 and 45 disaccharide units were added during a 30 min incubation period. However, if incubation was con-tinued for up to 120 min (in the presence of IOO pg benzylpenicillin ml-l) a con-siderable amount of the newly synthesized peptidoglycan was lost from the purified wall because autolytic enzymes were expressed in the wall + membrane preparation after the action of the antibiotic