Kinetic studies on the esterase activity of cytoplasmic sheep liver aldehyde dehydrogenase.
Kinetic studies on the esterase activity of cytoplasmic sheep liver aldehyde dehydrogenase.
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细胞质羊肝醛脱氢酶酯酶活性的动力学研究
作者：
A. MacGibbon;S. Haylock;P. Buckley;L. Blackwell
采用稳态和瞬时动力学技术研究了羊肝细胞质醛脱氢酶（EC 1.2.1.3）催化乙酸对硝基苯酯的水解。NAD+和NADH刺激酯水解的稳态速率在预期的浓度的基础上，从脱氢酶反应的米氏常数。在较高浓度的辅酶，NAD+和NADH抑制反应竞争性相对于4-硝基苯乙酸，抑制常数分别为104和197微米。丙醛和水合氯醛是酯酶反应的竞争性抑制剂。观察到4-硝基苯氧离子产生的爆发，速率常数为12 +/- 2s-1，爆发幅度为基于已知NADH结合位点浓度预期的30%。酯酶反应的限速步骤发生在4-硝基苯氧离子形成之后。参数的存在下，不同的酯和脱乙酰基结合位点。
The hydrolysis of 4-nitrophenyl acetate catalysed by cytoplasmic aldehyde dehydrogenase (EC 1.2.1.3) from sheep liver was studied by steady-state and transient kinetic techniques. NAD+ and NADH stimulated the steady-state rate of ester hydrolysis at concentrations expected on the basis of their Michaelis constants from the dehydrogenase reaction. At higher concentrations of the coenzymes, both NAD+ and NADH inhibited the reaction competitively with respect to 4-nitrophenyl acetate, with inhibition constants of 104 and 197 micron respectively. Propionaldehyde and chloral hydrate are competitive inhibitors of the esterase reaction. A burst in the production of 4-nitrophenoxide ion was observed, with a rate constant of 12 +/- 2s-1 and a burst amplitude that was 30% of that expected on the basis of the known NADH-binding site concentration. The rate-limiting step for the esterase reaction occurs after the formation of 4-nitrophenoxide ion. Arguments are presented for the existence of distinct ester- and aldehyde-binding sites.