Role of the Penicillin-Sensitive Transpeptidation Reaction in Attachment of Newly Synthesized Peptidoglycan to Cell Walls of Micrococcus luteus

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Abstract
Cell-wall preparations of Micrococcus luteus ( lysodeikticus ) catalyze in vitro peptidoglycan synthesis from UDP N -acetyl-D-glucosamine, UDP N -acetylmuramic acid-pentapeptide, and glycine. Newly synthesized peptidoglycan is partially cross-linked by a transpeptidation reaction with concomitant release of C-terminal D-alanine. Penicillin not only strongly inhibits release of D-alanine (98% at 1 μg/ml), but also markedly inhibits incorporation of acetylglucosamine and N -acetylmuramic acid-pentapeptide into the preformed cell-wall peptidoglycan. The simplest explanation for the results is that incorporation of newly synthesized strands of peptidoglycan and their attachment to “older” cell-wall peptidoglycan proceeds mainly by transpeptidation and that transglycosylation is responsible only for part of the elongation of the pre-existing peptidoglycan. Another possibility is that incorporation occurs by transglycosylation, but it cannot continue without concurrent formation of peptide cross-bridges.