[大鼠肝脏低温切片中肌苷-5-单磷酸脱氢酶和5'-核苷酸酶反应动力学的定量组织化学研究]

[Quantitative histochemical study of the reaction kinetics to inosine-5-monophosphate dehydrogenase and 5'-nucleotidase in cryostat sections of rat liver].

作者信息

Grushetskaia N V, Prianishnikov V A

出版信息

Tsitologiia. 1983 Jul;25(7):805-10.

Abstract

The data are presented on kinetics of histochemical enzymatic reactions demonstrating two enzymes taking part in the purine metabolism--inosine-5-monophosphate dehydrogenase (IMPD) and 5'-nucleotidase (5'-NT). It is shown that IMPD has a very weak affinity to substrate IMP (KM = 2.5 . 10(-2) M); this fact partially explains the low rate course in cryostat sections. Cytosol and membrane forms of 5'-NT have the maximum affinity to AMP (KM for membrane and cytosol forms being 1 . 10(-3) M and 2.1 . 10(-3) M, resp.). When IMP is used as a substrate, 5'-NT localized in cytosol has much lower KM as compared to the membrane form. Cytoplasmic 5'-NT is thermostable. It is suggested that a low rate of histochemical reaction demonstrating IMPD is caused by a degradation of substrate by the membrane form of 5'-NT, the Michaelis constant of which is 5 times less than that of IMPD.

摘要

本文展示了组织化学酶促反应的动力学数据，该反应涉及参与嘌呤代谢的两种酶——肌苷-5-单磷酸脱氢酶（IMPD）和5'-核苷酸酶（5'-NT）。结果表明，IMPD对底物IMP的亲和力非常弱（KM = 2.5×10⁻² M）；这一事实部分解释了冰冻切片中反应速率较低的原因。5'-NT的胞质溶胶形式和膜形式对AMP具有最大亲和力（膜形式和胞质溶胶形式的KM分别为1×10⁻³ M和2.1×10⁻³ M）。当IMP用作底物时，与膜形式相比，位于胞质溶胶中的5'-NT的KM要低得多。细胞质中的5'-NT具有热稳定性。有人认为，显示IMPD的组织化学反应速率较低是由于5'-NT的膜形式对底物的降解所致，其米氏常数比IMPD的米氏常数小5倍。