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Abstract
SUMMARY: A wall + membrane preparation from Micrococcus luteus 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 β-elimination. Benzylpenicillin (1 µg ml−1) inhibited cross-linking but not overall synthesis of glycan whereas at concentrations above 10 µg ml−1 overall glycan synthesis was slightly inhibited. In the presence of 100 µ;g benzylpenicillin ml−1 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 continued for up to 120 min (in the presence of 100 µg benzylpenicillin ml−1) a considerable 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.
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