锂离子和钠离子对酵母烯醇化酶的抑制作用1。

The inhibition of yeast enolase by Li+ and Na+1.

作者信息

Kornblatt M J, Musil R

机构信息

Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada.

出版信息

Arch Biochem Biophys. 1990 Mar;277(2):301-5. doi: 10.1016/0003-9861(90)90583-k.

DOI:10.1016/0003-9861(90)90583-k

PMID:2178554

Abstract

The activity of yeast enolase is inhibited by Li+ and Na+. At pH 7.1, inhibition by Li+ is "mixed" with respect to Mg2+; both Vmax and Km (Mg2+) are increased by Li+. The inhibition by Li+ appears to be partial, indicating that enzyme with Li+ bound is active. The step inhibited by Li+ cannot be proton abstraction since Li+ decreases the kinetic isotope effect on Vmax. At pH 9.2, where proton abstraction is no longer partially rate-limiting, inhibiton by Li+ is competitive with respect to Mg2+. The rate of enzyme-catalyzed exchange of the C-2 hydrogen with solvent is not affected by Li+. We interpret these results as follows: Li+ (and Na+) binds to enolase and decreases the rate of at least one step in the mechanism. At pH 7.1, this step is partially rate-limiting; at pH 9.2, this step is a fast step in the reaction. The step inhibited by Li+ cannot be proton abstraction but may be release of product (phosphoenol pyruvate) or Mg2+.

摘要

酵母烯醇化酶的活性受到Li⁺和Na⁺的抑制。在pH 7.1时，Li⁺对Mg²⁺而言表现为“混合型”抑制；Li⁺会使Vmax和Km（Mg²⁺）均升高。Li⁺的抑制作用似乎是部分性的，这表明结合了Li⁺的酶仍具有活性。Li⁺所抑制的步骤不可能是质子提取，因为Li⁺会降低对Vmax的动力学同位素效应。在pH 9.2时，此时质子提取不再是部分限速步骤，Li⁺的抑制作用对Mg²⁺而言是竞争性的。酶催化的C-2氢与溶剂的交换速率不受Li⁺影响。我们对这些结果的解释如下：Li⁺（和Na⁺）与烯醇化酶结合并降低了反应机制中至少一个步骤的速率。在pH 7.1时，该步骤是部分限速步骤；在pH 9.2时，该步骤是反应中的快速步骤。Li⁺所抑制的步骤不可能是质子提取，但可能是产物（磷酸烯醇丙酮酸）或Mg²⁺的释放。