等温滴定量热法测定脲酶催化尿素水解反应动力学

Kinetics of urease-catalyzed hydrolysis reaction of urea determined by isothermal titration calorimetry

采用等温滴定量热法研究脲酶催化尿素的水解反应(尿素浓度147mmol·L-1,脲酶浓度3.0×10-7mmol·L-1,pH=7.0磷酸缓冲溶液)动力学,测定了该反应在298.15～318.15K温度范围内的反应速率常数kcat和米氏常数Km等动力学参数.结果表明:在实验条件下,脲酶催化尿素的水解反应符合Michaelis-Menten机理;温度对kcat的影响遵循阿累尼乌斯方程,表观活化能为16.6kJ·mol-1;等温滴定量热法可有效地用于酶催化反应动力学参数的测定,是具有应用前景的研究酶活性的方法.

Isothermal titration calorimetry （ITC） was used to observe the enzyme-catalyzed hydrolysis reaction of urea. Two kinetic parameters, the enzymatic conversion rate constant, kcat, and the Maichaelis constant, Km, for the urea （147 mmol · L^-1） / urease （3.0）〈 10 7 mmol· L^-1） enzymatic system in sodium phosphate buffer at pH 7.0 at T=（298.15 to 318.15）K were determined from the isothermal titration calorimetry experimental data. The results indicated that the urease-catalyzed reaction approximated well to the Michaelis-Menten equation under the experimental conditions. The effect of the temperature on the variation of the values of kcat can be correlated quantitatively to the Arrhenius equation with the apparent activation energy of 16.6 kJ ·mol^-1. The results showed a good example of effectively evaluating kinetic parameters for enzyme-catalyzed reaction by ITC. It is suggested that ITC should he suitable and have significant potential for the kinetic study of enzyme activity.