Di Donato A, Piccoli R, D'Alessio G
Biochem J. 1987 Jan 15;241(2):435-40. doi: 10.1042/bj2410435.
Binding of nucleotides to bovine seminal RNAase was studied by differential spectrophotometry and equilibrium dialysis. Cytidine 3'-phosphate, the reaction product of the hydrolytic, rate-limiting step of the reaction, was found to be capable, in contrast to related nucleotides, of discriminating between the two structurally identical active sites of the enzyme. Negative co-operativity, with a 'half-of-sites' reactivity, was found at lower concentrations of ligand, whereas at higher concentrations positive co-operativity was detected. These findings exclude that the non-hyperbolic kinetics previously reported for the hydrolytic step of the reaction are due to hysteretic effect. A model of mixed-type co-operativity is proposed for interpreting the binding data.
通过差示分光光度法和平衡透析法研究了核苷酸与牛精液核糖核酸酶的结合。与相关核苷酸相比，发现反应水解限速步骤的反应产物3'-磷酸胞苷能够区分该酶的两个结构相同的活性位点。在较低配体浓度下发现具有“半位点”反应性的负协同性，而在较高浓度下检测到正协同性。这些发现排除了先前报道的该反应水解步骤的非双曲线动力学是由于滞后效应的可能性。提出了一种混合型协同性模型来解释结合数据。
