Effect of Extraneous Zinc on Calf Intestinal Alkaline Phosphatase

The effect of extraneous zinc on calf intestinal alkaline phosphatase was studied for quick reversible binding and slow irreversible binding of zinc ions at various concentrations. Under the conditions of slow binding of zinc to CIP increasing Zn2+ (less than 1.0 mM, nM/nE 1.0 × 106) inhibited enzymatic activity, and further increasing Zn2+ resulted in an increase of activity. For quick reversible binding of Zn2+, the effect on CIP activity changed at lower concentrations of substrate, indicating a complex cooperativity between Zn2+ and pNPP. Both protein intrinsic emission fluorescence and ANS-bound protein fluorescence, as well as circular dichroism spectra have shown that the binding of zinc ions changed the enzyme conformation, which was the reason for the changes in enzyme activity induced by extraneous zinc.