Gates C A, Northrop D B
Division of Pharmaceutical Biochemistry, School of Pharmacy, University of Wisconsin, Madison 53706.
Biochem Biophys Res Commun. 1988 Apr 15;152(1):406-10. doi: 10.1016/s0006-291x(88)80728-9.
Alternative substrates, such as those isotopically-labeled, which differ in their rate constants of catalysis but not in their rate constants of binding, generate identical values of V/Ka in ordered kinetic mechanisms of bireactant enzymes. This is shown to be true even for the rapid-equilibrium ordered mechanism in which an abortive complex between free enzyme and the second substrate is formed. In contrast, rapid-equilibrium random mechanisms have non-identical values for V/Ka. Consequently, the effect of alternative substrates or isotope effects on V/Ka provides a means to distinguish between these nearly identical kinetic mechanisms.
替代性底物，例如那些同位素标记的底物，它们的催化速率常数不同，但结合速率常数相同，在双反应物酶的有序动力学机制中会产生相同的V/Ka值。即使对于自由酶与第二种底物之间形成无效复合物的快速平衡有序机制，这一点也被证明是正确的。相比之下，快速平衡随机机制的V/Ka值并不相同。因此，替代性底物或同位素效应对V/Ka的影响提供了一种区分这些几乎相同的动力学机制的方法。
