A theoretical study on nitric oxide reductase activity in a ba3-type heme-copper oxidase

被引:45
作者
Blomberg, LM [1 ]
Blomberg, MRA [1 ]
Siegbahn, PEM [1 ]
机构
[1] Univ Stockholm, Dept Phys, SE-10691 Stockholm, Sweden
来源
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS | 2006年 / 1757卷 / 01期
关键词
nitric oxide reductase; NOR; heme-copper oxidase; cytochrome c oxidase; CcO; reduction; electron transfer; nitrous oxide; nitric oxide; DFT; B3LYP;
D O I
10.1016/j.bbabio.2005.11.004
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The mechanism of nitric oxide reduction in a ba(3)-type heme-copper oxidase has been investigated using density functional theory (B3LYP). Four possible mechanisms have been studied and free energy surfaces for the whole catalytic cycle including proton and electron transfers have been constructed by comparison to experimental data. The first nitric oxide coordinates to heme a(3) and is partly reduced having some nitroxyl anion character ((NO-)-N-3), and it is thus activated toward the attack by the second NO. In this reaction step a cyclic hyponitrous acid anhydride intermediate with the two oxygens coordinating to Cu-beta, is formed. The cyclic hyponitrous acid anhydride is quite stable in a local minimum with high barriers for both the backward and forward reactions and should thus be observable experimentally. To break the N - O bond and form nitrous oxide, the hyponitrous acid anhydride must be protonated, the latter appearing to be an endergonic process. The endergonicity of the proton transfer makes the barrier of breaking the N - O bond directly after the protonation too high. It is suggested that an electron should enter the catalytic cycle at this stage in order to break the N - O bond and form N2O at a feasible rate. The cleavage of the N - O bond is the rate limiting step in the reaction mechanism and it has a barrier of 17.3 kcal/mol, close to the experimental value of 19.5 kcal/mol. The overall exergonicity is fitted to experimental data and is 45.6 kcal/mol. (c) 2005 Elsevier B.V. All rights reserved.
引用
收藏
页码:31 / 46
页数:16
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