Studies of Reversible Inhibition, Irreversible Inhibition and Activation of Alkaline Phosphatase by Capillary Electrophoresis

Reversible inhibition, irreversible inhibition, and activation of calf intestinal alkaline phosphatase (EC 3.1.3.1) have been studied by capillary electrophoresis. The capillary electrophoretic enzyme-inhibitor assays were performed by electrophoretically mixing zones of inhibitor and enzyme in a substrate-filled capillary. Enzyme inhibition was indicated by a decrease in product formation detected in the capillary by laser-induced fluorescence. Reversible enzyme inhibitors could be quantified by Michaelis-Menten treatment of the electrophoretic data. Reversible, competitive inhibition of alkaline phosphatase by sodium vanadate and sodium arsenate has been examined. The calculated K_i value for the capillary electrophoretic enzyme-inhibitor assays was 2.1 µM for sodium vanadate and 21 µM for sodium arsenate. The limit of detection for sodium vanadate was 3 µM, and the limit of detection for sodium arsenate was 10 µM. Reversible, non-competitive inhibition of alkaline phosphatase by theophylline has been studied. The calculated K_i value for the capillary electrophoretic enzyme-inhibitor assays for theophylline was 102 µM, and the limit of detection was 3 µM. Irreversible inhibition of alkaline phosphatase by EDTA at concentrations of 1.0 mM or higher has been observed. Activation of alkaline phosphatase has also been observed for EDTA at concentrations from 20 to 400 µM.