Penicillin-Binding Proteins of Bacteria
The penicillin-binding components of bacteria are presumably enzymes of cell wall peptidoglycan synthesis, and one or more of these is a presumed killing site for penicillins. All organisms which have so far been examined contain multiple penicillin-binding components, e.g., there are five in Bacillus subtilis, six in Escherichia coli, and four in Staphylococcus aureus. Progress in studying these components includes: 1) The demonstration that the hydroxylamine-induced release of penicillin G from several penicillin-binding components is enzymatically catalyzed. In addition, the effect of sulfhydryl reagents on the catalytic and penicillin binding activities of E. coli carboxypeptidase IA suggests that a thiol group is involved in a deacylation reaction of the enzyme. 2) One of the S. aureus binding components can be isolated by affinity chromatography based on the reversibility of its penicillin binding. Under appropriate conditions it can catalyze transpeptidase, carboxypeptidase and penicillinase activities. 3) Altered penicillin-binding components are found in mutants of B. subtilis which have been isolated as step-wise penicillin-resistant organisms, 4) The penicilloyl residue of the penicillin-binding components is released at a slow rate in a novel, enzymatically catalyzed degradation. The products of this degradation in the case of the B. stearothermophilus D-alanine carboxypeptidase have been identified as phenylacetylglycine and 5,5-dimethylthiazoline carboxylic acid.
KeywordsThiol Group Penicillin Resistance Killing Site Carboxypeptidase Activity Bacterial Cell Wall Synthesis
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