Acquisition of substrate specific parameters during the catalytic reaction of penicillinase

The progress of the catalytic reaction of penicillinase (EC 3.5.2.6; penicillin amido β lactamhydrolase) from Bacillus cereus depends on the structure of the side chain in derivatives of 6 aminopenicillanic acid (the parent substrate). Side chains of one class promote the rate of the reaction and cause no deviation from the linear kinetics observed with the parent compound. By contrast, side chains of the other class induce a time dependent, reversible change in the parameters of the catalytic reaction. The rate decelerates considerably and then becomes constant; the decrease in K(cat) is accompanied by a corresponding decrease in K(m). The initial parameters of the biphasic reaction, determined by stopped flow spectrophotometry, approach those of the unsubstituted 6 aminopenicillanic acid. The final parameters, which are specific for each derivative, are not acquired when the native conformation of the enzyme is stabilized by homologous antibodies.