Walker E J, Ralston G B, Darvey I G
Biochem J. 1975 Jun;147(3):425-33. doi: 10.1042/bj1470425.
Data from two assay systems show that the kinetics of the hydrolysis of cytidine 2':3'-cyclic monophosphate by bovine pancreatic RNAase (ribonuclease) is not consistent with conventional models. An allosteric model involving a substrate-dependent change in the equilibrium between two enzyme conformations is proposed. Such a model gives rise to a calculated curve of velocity versus substrate concentration which fits the experimental data. The model is also consistent with the results of an examination of the tryptic digestion of RNAase. Substrate analogues are able to protect RNAase against hydrolysis by trypsin and the percentage of RNAase activity which remains after digestion increases sigmoidally as the analogue concentration is increased. The model also explains the pattern seen in the Km values quoted in the literature and is consistent with strong physical evidence for a ligand-induced conformational change for RNAase reported in the literature.
来自两个分析系统的数据表明，牛胰核糖核酸酶对胞苷2':3'-环一磷酸的水解动力学与传统模型不一致。提出了一种变构模型，该模型涉及两种酶构象之间平衡的底物依赖性变化。这样的模型产生了一条计算出的速度与底物浓度的曲线，该曲线与实验数据相符。该模型也与核糖核酸酶胰蛋白酶消化研究的结果一致。底物类似物能够保护核糖核酸酶不被胰蛋白酶水解，并且消化后剩余的核糖核酸酶活性百分比随着类似物浓度的增加呈S形增加。该模型还解释了文献中引用的米氏常数（Km值）所呈现的模式，并且与文献中报道的核糖核酸酶配体诱导构象变化的有力物理证据一致。
