Isatin inhibition of rat testicular alkaline phosphatase. A non-allosteric phenomenon.

Isatin has been found to inhibit rat testicular alkaline phosphatase (EC 3.1.3.1) uncompetitively. The hyperbolic curve relating inhibition as a function of substrate concentration; the persistence of inhibition after the tertiary structure of the enzyme has been altered by heat denaturation, exposure to urea or papain digestion; the small changes in entropy, free energy and enthalpy in the presence of isatin, and the number of isatin molecules (n = 1.29) combining with one molecule of enzyme indicate the non-allosteric nature of inhibition.