来自大肠杆菌的尿苷磷酸化酶。动力学性质及作用机制。

Uridine phosphorylase from Escherichia coli. Kinetic properties and mechanism.

作者信息

Krenitsky T A

出版信息

Biochim Biophys Acta. 1976 Apr 8;429(2):352-8. doi: 10.1016/0005-2744(76)90283-7.

Abstract

Type I and Type II uridine phosphorylases (uridine: orthophosphate ribosyltransferase EC 2.4.2.3) are distinguished by their pH optima (Krenitsky et al. (1965) J. Biol. Chem. 240, 1281-1286). A Type I enzyme was partially purified from Escherichia coli. The crossing pattern of the initial velocity analysis indicated that the catalytic mechanism involved the sequential addition of substrates to the enzyme. Product inhibition by uracil or by ribose 1-phosphate was linear competitive with uridine or with concentrations of phosphate below 3 mM. This indicated that the sequence of substrate addition was random rather than ordered. At concentrations of phosphate above 3 mM, product inhibition by uracil was complex. The random mechanism of this Type I enzyme contrasts with the ordered mechanism of a Type II enzyme from rat liver (Kraut, A. and Yamada, E.W. (1971) J. Biol. Chem. 246, 2021-2030).

摘要

I型和II型尿苷磷酸化酶（尿苷：正磷酸核糖基转移酶，EC 2.4.2.3）可通过其最适pH值加以区分（Krenitsky等人，《生物化学杂志》，第240卷，第1281 - 1286页，1965年）。从大肠杆菌中部分纯化出了一种I型酶。初始速度分析的交叉模式表明，催化机制涉及底物依次添加到酶上。尿嘧啶或1 - 磷酸核糖对产物的抑制作用与尿苷或浓度低于3 mM的磷酸盐呈线性竞争关系。这表明底物添加顺序是随机的而非有序的。在磷酸盐浓度高于3 mM时，尿嘧啶对产物的抑制作用较为复杂。这种I型酶的随机机制与大鼠肝脏II型酶的有序机制形成对比（Kraut, A.和Yamada, E.W.，《生物化学杂志》，第246卷，第2021 - 2030页，1971年）。