KINETICS OF INACTIVATION OF GREEN CRAB (SCYLLA-SERRATA) ALKALINE-PHOSPHATASE DURING REMOVAL OF ZINC IONS BY ETHYLENEDIAMINETETRAACETIC ACIDDISODIUM

Green crab (Scylla Serrata) alkaline phosphatase (EC 3.1.3.1.) is a me talloenzyme, the each active site in which contains a tight cluster of two zinc ions and one magnesium ion. The kinetic theory of the substr ate reaction during irreversible inhibition of enzyme activity previou sly described by Tsou has been applied to a study on the kinetics of t he course of inactivation of the enzyme by ethylenediaminetetraacetic acid disodium (EDTA). The kinetics of the substrate reaction with diff erent concentrations of the substrate p-nitrophenyl phosphate (PNPP) a nd inactivator EDTA suggested a complexing mechanism for inactivation by, and substrate competition with, EDTA at the active site. The inact ivation kinetics are single phasic, showing the initial formation of a n enzyme-EDTA complex is a relatively rapid reaction, followed a slow inactivation step that probably involves a conformational change of th e enzyme. Zinc ions are finally removed from the enzyme. The presence of metal ions apparently stabilizes an active-site conformation requir ed for enzyme activity. Copyright (C) 1996 Elsevier Science B.V.