No abstract

No abstract

The interactions of Mg 2+ and Zn 2+ ions in the activation of non-specific tissue alkaline phosphatase were investigated using crude extracts of rat kidney. Activation of alkaline phosphatase by the metal ions was accompanied by changes in the kinetic parameters of p- INTRODUCTIONThe roles of metal ions in metalloenzymes include direct participation in catalysis, stabilization of protein structure and regulation of enzymatic activity. Membrane alkaline phosphatase (ALP) is a metal-containing enzyme that serves as a good model for the study of metal ion interactions in enzyme catalysis. Native E. coli ALP contains three metal ion binding sites (two Zn 2+ sites and one Mg 2+ site), and studies on their roles and interrelationships have provided some insights into the mechanism of the enzyme 1 . E. coli ALP is a zinc metalloenzyme, which can be activated by magnesium ion 2 . Removal of the Zn 2+ leads to loss of catalytic activity while its replacement by other divalent cations (Mn 2+ , Co 3+ , Cd 2+ , and Cu 2+ ) resulted in lower maximal activity 2 . It has been shown that while low concentrations of Mg 2+ stimulated the refolding of E. coli ALP, high concentration actually inhibited its reconstitution into the active form 3 . This suggests that Mg 2+ mediates stabilization and destabilization of the catalytically active structure of ALP at low and high concentrations respectively 4,5 . In E. coli ALP, Mg 2+ is thought to have a regulatory effect on the expression of catalytic activity and maintenance of structural integrity of the enzyme 1 . The specific binding of Mg 2+ to apo-ALP depends on both pH and the cooperative effects of Zn 2+ binding. Mg 2+ alone does not confer catalytic activity on ALP, but it does regulate the Zn 2+ -induced restoration of activity and perhaps, structural integrity of the metal-binding loci 1,6 .

No abstract

No abstract