Isatin-enzyme interactions. VII. Mechanism of inhibition of rat kidney alkaline phosphatase.

Isatin has been found to inhibit rat kidney alkaline phosphatase (EC 3.1.3.1). The inhibition is dependent on isatin concentration and is of un-competitive type. The hydrolysis of disodium phenyl phosphate by the enzyme at different temperatures (17--37 degrees C) obeys the Arrhenius equation. Energy of activation in the absence and presence of isatin has been found to be 9.84 and 10.24 kCal/mol. The hyperbolic profile of isatin inhibition; the lowering of both Km and Vmax in the presence of isatin, and, small changes in enthalpy, free energy and entropy in the presence of isatin suggest a non-allosteric un-competitive inhibition of the enzyme.