内消旋酒石酸盐对马铃薯“苹果酸”酶的单向抑制和激活作用
Unidirectional inhibition and activation of "malic' enzyme of Solanum tuberosum by meso-tartrate.
作者信息
Do Nascimento K H, Davies D D, Patil K D
出版信息
Biochem J. 1975 Aug;149(2):349-55. doi: 10.1042/bj1490349.
A kinetic study of "malic' enzyme (EC 1.1.1.40) from potato suggests that the mechanism is Ordered Bi Ter with NADP+ binding before malate, and NADPH binding before pyruvate and HCO3-. The analysis is complicated by the non-linearity that occurs in some of the plots. meso-Tartrate is shown to inhibit the oxidative decarboxylation of malate but to activate the reductive carboxylation of pyruvate. To explain these unidirectional effects it is suggested that the control site of "malic' enzyme binds organic acids (including meso-tartrate) which activate the enzyme. meso-Tartrate, however, competes with malate for the active site and thus inhibits the oxidative decarboxylation of malate. Because meso-tartrate does not compete effectively with pyruvate for enzyme-NADPH, its binding at the control site leads to a stimulation of the carboxylation of pyruvate. A similar explanation is advanced for the observation that malic acid stimulates its own synthesis.
对来自马铃薯的“苹果酸”酶（EC 1.1.1.40）的动力学研究表明，其机制为有序双底物乒乓机制，NADP⁺在苹果酸之前结合，NADPH在丙酮酸和HCO₃⁻之前结合。某些图中出现的非线性使分析变得复杂。内消旋酒石酸盐被证明可抑制苹果酸的氧化脱羧，但可激活丙酮酸的还原羧化。为了解释这些单向效应，有人提出“苹果酸”酶的控制位点结合有机酸（包括内消旋酒石酸盐），这些有机酸可激活该酶。然而，内消旋酒石酸盐与苹果酸竞争活性位点，从而抑制苹果酸的氧化脱羧。由于内消旋酒石酸盐与丙酮酸对酶 - NADPH的竞争效果不佳，其在控制位点的结合导致丙酮酸羧化的刺激。对于苹果酸刺激自身合成的观察结果也提出了类似的解释。
Zotero 插件