title: Acquisition of substrate-specific parameters during the catalytic reaction of penicillinase.
abstract: The progress of the catalytic reaction of penicillinase (EC 3.5.2.6; penicillin amido-beta-lactamhydrolase) 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 kcat is accompanied by a corresponding decrease in Km. 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.
mesh_terms: D000906:Antibodies; D000937:Antigen-Antibody Reactions; D001409:Bacillus cereus / Q000201:enzymology; D001665:Binding Sites; D007700:Kinetics; D010405:Penicillinase / Q000276:immunology / Q000378:metabolism*; D010406:Penicillins / Q000378:metabolism*; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D000906:Antibodies; D010406:Penicillins; D010405:Penicillinase