ON THE ROLE OF THE HIGH-MOLECULAR-WEIGHT PENICILLIN-BINDING PROTEINS IN THE CELL-CYCLE OF ESCHERICHIA-COLI

Blocking of penicillin-binding proteins (PBP) 2 or 3 of Escherichia coli by specific antibiotics led to inhibition of peptidoglycan synthesis measured as rate of H-3-Dap incorporation. The inhibition was ca 60% by mecillinam (blocking PBP2) and ca 35% by cephalexin or furazlocillin (both specific for PBP3). PBP3 could be inhibited primarily during constriction, whereas the inhibition of PBP2 was observed throughout the cell cycle. The ratio of PBP2 and 3 activities appeared to be correlated with cell shape, i.e. in long rods, inhibition of peptidoglycan synthesis by mecillinam was stronger than in short rods. Inhibition studies with the PBP1A/1B-specific antibiotic cefsulodin showed that, with a delay of approximately 1/2 mass-doubling time, peptidoglycan synthesis was inhibited completely with concomitant lysis. The cefsulodin-induced lysis was independent of the stage of the cell cycle. It was suggested that PBP1A/1B do not have a specific function in either elongation or constriction. Rather, they seem to have a general activity on the basis of which the other synthesizing PBP perform their special tasks. This interpretation is formulated as a "primer model of peptidoglycan synthesis".