d-Alanine Carboxypeptidase from Bacillus subtilis Membranes

The purified d-alanine carboxypeptidase isolated from Bacillus subtilis was irreversibly inactivated by penicillin G and other β-lactam antibiotics. The reaction involved an initial reversible binding step followed by an irreversible step. Both the reversible binding constant (Ki) and the rate constant for irreversible inactivation (k3) were determined for a number of β-lactam antibiotics. In general Ki varied among these antibiotics much more than k3. Significant differences were also observed in the Ki for the pure soluble enzyme and that for the membrane bound enzyme; these differences might be attributable to the solubility of the β-lactam antibiotic in the membrane phase.