蝇蕈醇与4-氨基丁酸转氨酶的反应。

Reaction of muscimol with 4-aminobutyrate aminotransferase.

作者信息

Fowler L J, Lovell D H, John R A

出版信息

J Neurochem. 1983 Dec;41(6):1751-4. doi: 10.1111/j.1471-4159.1983.tb00889.x.

DOI:10.1111/j.1471-4159.1983.tb00889.x

Abstract

The reaction of muscimol as amino donor substrate for GABA transaminase (GABA-T) has been studied using enzyme purified from rabbit brain. Enzyme activity was assayed by measuring the glutamate produced using glutamate dehydrogenase. Kinetic parameters determined at 37 degrees C were for GABA, Km (app) = 1.92 +/- 0.24 mM, specific activity = 7.33 +/- 0.27 mumol/min/mg (kcat = 13.7s-1), and for muscimol, Km (app) = 1.27 +/- 0.15 mM, specific activity = 0.101 +/- 0.009 mumol/min/mg (kcat = 0.19s-1). Addition of muscimol to the enzyme caused the spectral changes associated with conversion of the pyridoxaldimine form to the pyridoxamine form, and the first-order rate constant for the reaction showed a dependence on muscimol concentration that followed saturation kinetics, with a K = 1.1 +/- 0.18 mM and kmax = 0.065 +/- 0.004 s-1 (19 degrees C). The rate of spectral change observed on addition of muscimol to ornithine transaminase was extremely slow--at least an order of magnitude slower than that seen with GABA-T.

摘要

已使用从兔脑纯化的酶研究了蝇蕈醇作为γ-氨基丁酸转氨酶（GABA-T）氨基供体底物的反应。通过使用谷氨酸脱氢酶测量产生的谷氨酸来测定酶活性。在37℃下测定的动力学参数，对于GABA，Km（表观）= 1.92±0.24 mM，比活性 = 7.33±0.27 μmol/分钟/毫克（kcat = 13.7 s-1），对于蝇蕈醇，Km（表观）= 1.27±0.15 mM，比活性 = 0.101±0.009 μmol/分钟/毫克（kcat = 0.19 s-1）。向酶中添加蝇蕈醇会引起与吡哆醛亚胺形式转化为吡哆胺形式相关的光谱变化，并且该反应的一级速率常数显示出对蝇蕈醇浓度的依赖性，遵循饱和动力学，K = 1.1±0.18 mM，kmax = 0.065±0.004 s-1（19℃）。向鸟氨酸转氨酶中添加蝇蕈醇时观察到的光谱变化速率极慢——至少比GABA-T慢一个数量级。