L-天冬酰胺酶动力学参数的pH依赖性

pH dependence of the kinetic parameters of L-asparaginase.

作者信息

O'Leary M H, Mattes S L

出版信息

Biochim Biophys Acta. 1978 Jan 12;522(1):238-42. doi: 10.1016/0005-2744(78)90339-x.

Abstract

The concentration dependence of the rate of hydrolysis of L-asparagine by Escherichia coli L-asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) has been measured over the range pH 4.5 to pH 9.1 by a direct spectrophotometric assay at 220 nm and by a coupled assay utilizing glutamate dehydrogenase to detect the ammonia produced. The velocity of the hydrolysis reaction at saturating levels of substrate is independent of pH over this interval. The plot of V/km over the same interval is bell-shaped, being dependent on pKa values of 6.58 and 8.69. The higher pKa is attributed to the amino group of asparagine. The lower pKa is associated with the enzyme active site and is probably due to an imidazole group.

摘要

通过在220nm处的直接分光光度法测定以及利用谷氨酸脱氢酶检测产生的氨的偶联测定法，在pH 4.5至pH 9.1的范围内测量了大肠杆菌L-天冬酰胺酶（L-天冬酰胺酰胺水解酶，EC 3.5.1.1）对L-天冬酰胺水解速率的浓度依赖性。在该时间间隔内，底物饱和水平下的水解反应速度与pH无关。在相同时间间隔内V/km的曲线呈钟形，取决于6.58和8.69的pKa值。较高的pKa归因于天冬酰胺的氨基。较低的pKa与酶活性位点相关，可能是由于一个咪唑基团。