Add time:07/18/2019         Source:sciencedirect.com

Staphylococcal penicillinase (EC 3.5.2.6) is shown to undergo partial, fully reversible inactivation of benzylpenicillinase activity on incubation with the substrate quinacillin, the hydrolysis of which follows a corresponding biphasic time-course. The kinetics fit a scheme involving slow isomerization of the enzyme between conformational states that differ in Km and Vmax for quinacillin. The possibility that inactivation is related to formation of a previously observed covalent enzyme-quinacillin conjugate is ruled out because the kinetics of its formation differ from those of inactivation. This implies that the conjugate arises from a state of the enzyme substrate complex present during the normal catalytic cycle. The multiplicity of binding sites found suggests that a reactive catalytic intermediate substitutes several amino-acid side chains during denaturation of the enzyme-quinacillin mixture, thus providing an explanation of earlier results.

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