Enzyme deactivation.
Enzyme deactivation.
复制标题
酶失活。
作者：
A. Sadana
酶的失活动力学通常为一级动力学。不同的酶在不同的条件下表现出一级失活动力学的不同例子被提出。给出了可溶酶和固定化酶的例子。分析了不同参数、特定残基、抑制剂、钝化剂、保护剂的化学修饰、外部试剂诱导的构象变化、酶浓度以及不同底物对不同酶的一级失活动力学的影响。来自各个不同领域的不同例子提供了一个明智的框架和集合，证明了一级失活动力学的广泛适用性。文中还给出了可逆一级失活动力学和失活伪装动力学的例子。还提出了不同的机制来模拟复杂的酶失活。强调了非串联型机理，包括底物和化学修饰剂。给出了“可分离”和“不可分离”两种类型的依赖于底物的失活率表达式。给出了含有随时间变化的速率常数的速率表达式及其相应的机理。还给出了显示无失活宽限期的酶的例子。酶失活的一个有趣的例子是在自动腐烂的试剂存在的情况下失去活性。提出了一种求取本征失活速率常数的方法。给出了依赖于pH的酶失活的例子，可以用五步(或简化的两步)机制建模，也可以用涉及最终状态的剩余活性的单步机制来建模。在每种情况下都提供了适当的酶失活例子，以突出所涉及的不同机制。
Enzyme deactivation kinetics is often first-order. Different examples of first-order deactivation kinetics exhibited by different enzymes under a wide variety of conditions are presented. Examples of both soluble and immobilized enzymes are presented. The influence of different parameters, chemical modification of specific residues, inhibitors, inactivators, protecting agents, induced conformational changes by external agents, enzyme concentration, and different substrates on the first-order inactivation kinetics of different enzymes is analyzed. The different examples presented from a variety of different areas provides a judicious framework and collection demonstrating the wide applicability of first-order deactivation kinetics. Examples of reversible first-order deactivation kinetics and deactivation-disguise kinetics are also presented. Different mechanisms are also presented to model complex enzyme deactivations. The non-series type mechanisms are emphasized and these involve the substrate and chemical modifiers. Substrate-dependent deactivation rate expressions that are of "separable" and "non-separable" type are presented. Rate expressions involving time-dependent rate constants along with their corresponding mechanisms are presented. Examples of enzymes that exhibit a deactivation-free grace period are also given. An interesting case of enzyme inactivation is the loss of activity in the presence of an auto-decaying reagent. The method is presented by which the intrinsic inactivation rate constants may be obtained. Examples of pH-dependent enzyme inactivation are presented that may be modelled by a five-step (or a simplified two-step) mechanism, and also by a single-step mechanism involving residual activity for the final state. Appropriate examples of enzyme inactivation are presented in each case to highlight the different mechanisms involved.