Effect of penicillin on the in vivo formation of the D-alanyl-L-alanine peptide cross-linkage in cell walls of Micrococcus luteus.

Penicillin G was found to inhibit the formation of the d-alanyl-l-alanine cross-linkage in intact cells of Micrococcus luteus. This reaction was approximately 50-fold less susceptible to penicillin than the formation of the d-alanyl-l-lysine cross-linkage in the same organism. The presence of two penicillin-susceptible transpeptidation reactions that function in the incorporation of peptidoglycan precursors into the cell wall is proposed.