Qin Y, Cabral J M
Laboratório de Engenharia Bioquímica, Instituto Superior Técnico, Lisboa, Portugal.
Appl Biochem Biotechnol. 1994 Dec;49(3):217-40. doi: 10.1007/BF02783059.
The kinetics of urea hydrolysis catalyzed by urease, mainly in the absence of buffers by use of the self-buffer effect of the products, was investigated. The effect of pH, temperature, and concentration of enzyme, substrate, product, salt ions, and buffers on the kinetic behavior of urease was examined. A kinetic model of a modified Michaelis-Menten form, incorporating substrate and product inhibition, pH dependence, and temperature effect, was developed to describe the reaction rate. Experimental data indicated that urease in a buffer-free solution was less susceptible to the inhibition of substrate product. The Michaelis constant keeps almost constant with the variation of pH and temperature, and increases with the addition of buffers and salts. The data also suggested that the noncompetitive pattern of the product inhibition, which is not significantly affected by temperature, increases gently with increasing pH. A Monod form rate expression was proposed to analyze the pH effect on the maximum rate. The proposed kinetic model was also examined by the long-time experiments in which pH, substrate, and product concentration varied obviously during the reaction course.
研究了脲酶催化尿素水解的动力学，主要是在不使用缓冲液的情况下利用产物的自缓冲效应进行研究。考察了pH、温度以及酶、底物、产物、盐离子和缓冲液浓度对脲酶动力学行为的影响。建立了一个修正的米氏方程形式的动力学模型，该模型纳入了底物和产物抑制、pH依赖性以及温度效应，以描述反应速率。实验数据表明，无缓冲溶液中的脲酶对底物产物抑制的敏感性较低。米氏常数随pH和温度的变化几乎保持不变，但随缓冲液和盐的添加而增加。数据还表明，产物抑制的非竞争性模式不受温度显著影响，随pH升高而缓慢增加。提出了一个莫诺德形式的速率表达式来分析pH对最大速率的影响。还通过长时间实验对所提出的动力学模型进行了检验，在该实验中，反应过程中pH、底物和产物浓度有明显变化。
