甲胺脱氢酶至氨青素电子转移的底物激活证据。

Evidence for substrate activation of electron transfer from methylamine dehydrogenase to amicyanin.

作者信息

Davidson Victor L, Sun Dapeng

机构信息

Department of Biochemistry, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216-4505, USA.

出版信息

J Am Chem Soc. 2003 Mar 19;125(11):3224-5. doi: 10.1021/ja0297133.

DOI:10.1021/ja0297133

PMID:12630872

Abstract

Electron transfer (ET) from methylamine dehydrogenase (MADH) to amicyanin may be true or gated ET, depending upon the redox form of MADH. ET from the substrate-reduced aminoquinol form of MADH is gated, and the reaction rate is dependent on the presence of monovalent cations. This ET reaction has been studied in buffer free of monovalent cations. The reaction rate is orders of magnitude less than with saturating concentrations of monovalent cation. Analysis of the temperature dependence of this slow reaction, however, reveals that it is a true ET reaction. The rate of MADH reduction by substrate and the steady-state rate of substrate-dependent reduction of amicyanin by MADH were examined in different buffers. The results reveal that, in the steady state, the protonated methylammonium substrate performs the role previously attributed to monovalent cations in regulating the rate and mechanism of ET from MADH. The two putative cation binding sites previously observed in the crystal structure of MADH may now be assigned distinct roles, one as a catalytic substrate binding site and the other as a noncatalytic regulatory substrate binding site.

摘要

从甲胺脱氢酶（MADH）到蓝铜蛋白的电子转移（ET）可能是真实电子转移或门控电子转移，这取决于MADH的氧化还原形式。来自底物还原的氨基喹啉形式的MADH的电子转移是门控的，并且反应速率取决于单价阳离子的存在。此电子转移反应已在不含单价阳离子的缓冲液中进行研究。该反应速率比单价阳离子饱和浓度下的反应速率低几个数量级。然而，对这个缓慢反应的温度依赖性分析表明，它是一个真实的电子转移反应。在不同缓冲液中检测了底物对MADH的还原速率以及MADH对底物依赖性还原蓝铜蛋白的稳态速率。结果表明，在稳态下，质子化的甲铵底物发挥了先前归因于单价阳离子的作用，即在调节来自MADH的电子转移速率和机制方面。先前在MADH晶体结构中观察到的两个假定的阳离子结合位点现在可能被赋予不同的作用，一个作为催化底物结合位点，另一个作为非催化调节底物结合位点。