猪胃蛋白酶和鸡肝组织蛋白酶D对一些含有中性亲水基团的合成底物的水解动力学

The kinetics of hydrolysis of some synthetic substrates containing neutral hydrophilic groups by pig pepsin and chicken liver cathepsin D.

Irvine G B, Blumsom N L, Elmore D T

Biochem J. 1983 Apr 1;211(1):237-42. doi: 10.1042/bj2110237.

Abstract

Several peptides containing either of the sequences -Phe(NO2)-Trp- and -Phe(NO2)-Phe- and an uncharged hydrophilic group were synthesized, and the steady-state kinetics of their hydrolysis by pig pepsin (EC 3.4.23.1) and chicken liver cathepsin D (EC 3.4.23.5) were determined. Despite the presence of a hydrophilic group to increase substrate solubility, it was not possible to achieve the condition [S]0 much greater than Km, and, in some cases, only values of kcat./Km could be determined by measuring the first-order rate constant when [S]0 much less than Km. 2. Occupancy of the P2 and P3 sites considerably enhanced the specificity constant, and alanine was more effective than glycine at site P2. 3. The specificity constants for the hydrolysis by pepsin of those substrates in the present series that contain an amino acid residue at site P3 are considerably lower than for comparable substrates containing a cationic group. This difference does not apply to cathepsin D. 4. Hydrolyses with cathepsin D commonly exhibited a lag phase, and a possible explanation for this is given.

摘要

合成了几种含有-Phe(NO2)-Trp-和-Phe(NO2)-Phe-序列之一以及一个不带电荷的亲水基团的肽，并测定了它们被猪胃蛋白酶（EC 3.4.23.1）和鸡肝组织蛋白酶D（EC 3.4.23.5）水解的稳态动力学。尽管存在亲水基团以增加底物溶解度，但仍无法实现[S]0远大于Km的条件，并且在某些情况下，只有当[S]0远小于Km时通过测量一级速率常数才能确定kcat./Km的值。2. P2和P3位点的占据显著提高了特异性常数，并且在P2位点丙氨酸比甘氨酸更有效。3. 在本系列中那些在P3位点含有氨基酸残基的底物被胃蛋白酶水解的特异性常数远低于含有阳离子基团的可比底物。这种差异不适用于组织蛋白酶D。4. 组织蛋白酶D的水解通常表现出一个滞后阶段，并给出了对此的一种可能解释。