Reduced extent equations for kinetics of single-substrate product- inhibited enzyme-catalyzed reactions and mathematical model for thermokinetics have been suggested. By analyzing the thermograms of these reactions, this model can be conveniently used to calculate both kinetic parameters (K~m, K~i and V~m) and molar enthalpy (△~rH~m), and to establish the type of product inhibition simultaneously. Thermokinetics of arginase-catalyzed hydrolysis of L-arginine was studied by microcalorimetry, and the reaction product, L-ornithine, was established as a competitive reversible inhibitor. At 298.15K and pH 9.4, the K~i value for L-ornithine was 1.22×10^-^3mol·L^-^1. The reliability of this method for thermokinetics of single-substrate product-inhibited enzyme-catalyzed reactions has been verified by the experimental results.

Key words: ARGINASE, THERMODYNAMICS, MICROCALORIMETRIC METHOD