羧肽酶B在溶液和晶体中的动力学性质。

Kinetic properties of carboxypeptidase B in solutions and crystals.

作者信息

Alter G M, Leussing D L, Neurath H, Vallee B L

出版信息

Biochemistry. 1977 Aug 9;16(16):3663-8. doi: 10.1021/bi00635a024.

Abstract

The correlation of the structure of crystalline enzymes with their activities in solution assumes that the catalytic properties are identical in the two physical states. The present data demonstrate that in bovine carboxypeptidase B they differ significantly. Normal Michaelis-Menten kinetics characterize the hydrolysis of several esters and peptide substrates in both physical states. Crystallization reduces kcat 16 to 320-fold, while it affects KM variably and less dramatically. Small molecules inhibit catalytic activity both in solution and in crystals, but the carboxypeptidase inhibitor from potatoes (molecular weight 4200) does no inhibit the crystals. The activities of bovine carboxypeptidases A and B toward identical substrates are more similar in their crystals than in their solutions. This suggests that, over and above the structural dissimilarity of their crystals, conformational differences may additionally determine the activities of the two enzymes in solution. The findings demonstrate that the catalytic properties of carboxypeptidase B depend critically on its physical state.

摘要

晶体酶的结构与其在溶液中的活性之间的相关性假定催化特性在这两种物理状态下是相同的。目前的数据表明，对于牛羧肽酶B而言，它们存在显著差异。正常的米氏动力学表征了两种物理状态下几种酯和肽底物的水解情况。结晶使催化常数降低16至320倍，而它对米氏常数的影响则各不相同且影响较小。小分子在溶液和晶体中均抑制催化活性，但来自土豆的羧肽酶抑制剂（分子量4200）不抑制晶体。牛羧肽酶A和B对相同底物的活性在晶体中比在溶液中更相似。这表明，除了它们晶体结构的差异之外，构象差异可能还额外决定了这两种酶在溶液中的活性。这些发现表明，羧肽酶B的催化特性严重依赖于其物理状态。