Studies of the high molecular weight penicillin-binding proteins of Bacillus subtilis

Seven or eight penicillin-binding proteins (PBPs) were detected in Bacillus subtilis membranes. By introducing covalent affinity chromatography employing cephalosporins as ligands, milligram amounts of three high molecular weight PBPs (PBP 1 ab, Mr = 120,000; PBP 2b, Mr = 94,000; and PBP 4, Mr = 78,000) were obtained without any contamination of the major PBP 5, the D-alanine carboxypeptidase. Small amounts of pure PBP 2b could be isolated by manipulation of the affinity chromatography conditions. Structural and physical properties of these proteins as well as the generation of one major penicilloyl peptide from each PBP by digestion with pepsin suggest that each PBP is the product of a separate gene. No enzymatic activity could be found in mixtures of these high molecular weight PBPs employing substrates used for the transpeptidase and D-alanine carboxypeptidase assays in particulate membrane fractions.