London J W, Shaw L M, Fetterolf D, Garfinkel D
Biochem J. 1976 Sep 1;157(3):609-17. doi: 10.1042/bj1570609.
The initial-velocity kinetics of hog kidney gamma-glutamyltransferase were studied. Glutamate gamma-(4-nitroanilide) and its 3-carboxy derivative, glutamate gamma-(3-carboxy-4-nitroanilide), served as gamma-glutamyl donors, and glycylglycine as an acceptor. Reaction products were identified by paper chromatography and amino acid analysis. Inhibited Ping Pong mechanisms and a comprehensive initial- velocity expression were developed which account for the observed simultaneous gamma-glutamyl transfer and autotransfer, competitive inhibition by glycylglycine, and non-competitive inhibition by the carboxy donor. The validity of the proposed Ping Pong mechanisms are supported by enzyme-velocity data obtained with constant ratios of acceptor to donor concentrations. Kinetic constants were determined by a non-linear regression analysis. With glutamate gamma-(4-nitroanilide) as the donor, Michaelis constants for the donor, acceptor and donor-acting-as-acceptor are 1.87, 24.9, and 2.08 mM respectively. With glutamate gamma-(3-carboxy-4-nitroanilide) as the donor, these Michaelis constants are 1.63, 16.6, and 12.3 mM. Glyclyglycine competitive inhibition constants with the parent donor and its carboxy derivative are 275 and 205 mM respectively; the non-competitive inhibition constant of the carboxy donor is 34 mM.
对猪肾γ-谷氨酰转移酶的初速度动力学进行了研究。γ-谷氨酸-(4-硝基苯胺)及其3-羧基衍生物γ-谷氨酸-(3-羧基-4-硝基苯胺)作为γ-谷氨酰供体，甘氨酰甘氨酸作为受体。通过纸色谱法和氨基酸分析鉴定反应产物。建立了抑制性乒乓机制和一个全面的初速度表达式，该表达式解释了观察到的同时发生的γ-谷氨酰转移和自转移、甘氨酰甘氨酸的竞争性抑制以及羧基供体的非竞争性抑制。以受体与供体浓度恒定比例获得的酶速度数据支持了所提出的乒乓机制的有效性。通过非线性回归分析确定动力学常数。以γ-谷氨酸-(4-硝基苯胺)作为供体时，供体、受体和起受体作用的供体的米氏常数分别为1.87、24.9和2.08 mM。以γ-谷氨酸-(3-羧基-4-硝基苯胺)作为供体时，这些米氏常数分别为1.63、16.6和12.3 mM。甘氨酰甘氨酸对母体供体及其羧基衍生物的竞争性抑制常数分别为275和205 mM；羧基供体的非竞争性抑制常数为34 mM。
