Veríssimo Andreia F, Sousa Filipa L, Baptista António M, Teixeira Miguel, Pereira Manuela M
Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, Av. da República (EAN), 2781-901 Oeiras, Portugal.
Biochemistry. 2007 Nov 20;46(46):13245-53. doi: 10.1021/bi700733g. Epub 2007 Oct 27.
A comprehensive study of the thermodynamic redox behavior of the hemes from the cbb3 oxygen reductase from Bradyrhizobium japonicum was performed. This enzyme is a member of the C-type heme-copper oxygen reductase superfamily and has three subunits with six redox centers: four low-spin hemes and a high-spin heme and one copper ion, composing the site where oxygen is reduced. In this analysis, the visible spectra and redox properties of the five heme centers were deconvoluted. Their redox profiles and the pH dependence of the midpoint reduction potentials (redox-Bohr effect) were investigated. The reference reduction potentials (defined for a state where all centers are reduced) and homotropic interaction potentials were determined in the framework of a model of pairwise interacting redox centers. At pH 7.7, the reference reduction potentials for the three hemes c are 390, 300, and 220 mV, with low interaction potentials between them, weaker than -15 mV. For hemes b and b3, reference reduction potentials of 375 and 290 mV, respectively, were obtained; these two redox centers show an interaction potential weaker than -60 mV. The midpoint reduction potentials of all five hemes are pH-dependent. The study of these thermodynamic parameters is important in understanding the coupling mechanism of the redox and chemical processes during oxygen reduction. The analysis of the thermodynamic redox behavior of the cbb3 oxygen reductase contributes to the investigation of the mechanism of electron transfer and proton translocation by heme-copper oxygen reductases in general and indicates a thermodynamic coupling for the electron and proton transfer mechanisms.
对日本慢生根瘤菌cbb3氧还原酶中血红素的热力学氧化还原行为进行了全面研究。该酶是C型血红素-铜氧还原酶超家族的成员，有三个亚基和六个氧化还原中心：四个低自旋血红素、一个高自旋血红素和一个铜离子，构成氧还原的位点。在该分析中，对五个血红素中心的可见光谱和氧化还原性质进行了反褶积处理。研究了它们的氧化还原曲线以及中点还原电位的pH依赖性（氧化还原玻尔效应）。在成对相互作用的氧化还原中心模型框架内确定了参考还原电位（定义为所有中心均被还原的状态）和同促相互作用电位。在pH 7.7时，三个血红素c的参考还原电位分别为390、300和220 mV，它们之间的相互作用电位较低，弱于-15 mV。对于血红素b和b3，分别获得了375和290 mV的参考还原电位；这两个氧化还原中心的相互作用电位弱于-60 mV。所有五个血红素的中点还原电位均依赖于pH。对这些热力学参数的研究对于理解氧还原过程中氧化还原和化学过程的耦合机制很重要。对cbb3氧还原酶热力学氧化还原行为的分析有助于总体上研究血红素-铜氧还原酶的电子转移和质子转运机制，并表明电子和质子转移机制存在热力学耦合。
