异常的溶剂同位素效应在氨基酰化酶催化的乙酰氨基酸水解反应中。

Unusual solvent isotope effects on the aminoacylase-catalyzed hydrolysis of acetylamino acids.

作者信息

Henseling J, Röhm K H

出版信息

FEBS Lett. 1987 Jul 13;219(1):27-30. doi: 10.1016/0014-5793(87)81184-5.

Abstract

The deuterium solvent isotope effect on hydrolysis of acetylamino acids catalyzed by porcine kidney aminoacylase I (EC 3.5.1.14) was studied. With Ac-L-Met, a 'standard' aminoacylase substrate, the effect was normal at low pH (kcat(D)/kcat(H) = 0.7 at pH 6), virtually absent at neutrality, and distinctly inverse (kcat(D)/kcat(H) = 1.4) at pH 9. Km was not significantly affected. The rates of Ac-L-Phe hydrolysis in D2O considerably exceeded those in H2O at any pH between 6.5 and 9. We explain this unusual effect of D2O on aminoacylase I catalysis by an inverse equilibrium effect partially cancelling or, at high pH, reversing a normal isotope effect on kcat.

摘要

研究了氘代溶剂同位素效应对猪肾氨基酰化酶I（EC 3.5.1.14）催化的乙酰氨基酸水解的影响。对于“标准”氨基酰化酶底物Ac-L-Met，该效应在低pH时正常（pH 6时kcat(D)/kcat(H)=0.7），在中性时几乎不存在，而在pH 9时明显呈反向（kcat(D)/kcat(H)=1.4）。Km没有受到显著影响。在6.5至9之间的任何pH值下，D2O中Ac-L-Phe的水解速率都大大超过H2O中的水解速率。我们通过部分抵消或在高pH时逆转对kcat的正常同位素效应的反向平衡效应来解释D2O对氨基酰化酶I催化的这种异常效应。