Newly made enzymes determine ongoing cell wall synthesis and the antibacterial effects of cell wall synthesis inhibitors

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Abstract
Cell wall synthesis can continue with less than the total complement of cell wall synthetic enzymes present in normal growing cells. A method was developed to investigate whether there exists an excess of cell wall-synthesizing enzymes (penicillin-binding proteins [PBPs]) which all remain functional or whether a mixed population of functional and nonfunctional enzymes characterize normal cells. Surprisingly, cells in which less than 10% of the PBPs were functional could grow at a normal rate, as evidenced by increases in viable counts, culture turbidity, and rates of peptidoglycan, protein, and RNA synthesis. This subset of functional enzymes was biosynthetically new. Penicillin-induced lysis occurred contingent on the acylation of this same small fraction of PBPs, the copy number and affinities of which were below the level of detection by current fluorographic assay techniques. We propose that PBPs have a short functional half-life and that cell wall synthesis and bacterial lysis reflect the activity of newly synthesized PBPs.