Nicholls P
Department of Biological Sciences, Brock University, St. Catharines, Ont., Canada.
FEBS Lett. 1993 Jul 26;327(2):194-8. doi: 10.1016/0014-5793(93)80168-t.
Electron transfer to oxygen catalysed by cytochrome c oxidase is accompanied by spectral changes at the binuclear a3CuB centre, both in the soluble enzyme and in membranous systems, indicating spin or ligand state transitions of an iron that remains ferric. The other haem group, cytochrome a, does not change its spectral characteristics significantly during the steady state, but remains partially reduced until anaerobiosis. Cytochrome a3, is fully oxidized in each of its major steady state forms, and reduced upon anaerobiosis to a single ferrous species. Although cytochrome a is normally the immediate electron donor to the binuclear centre, its redox state does not alter under conditions in which the flux through the enzyme is changing significantly. A second electron transfer pathway to the binuclear centre may therefore exist, possibly one in which direct reduction of the binuclear a3CuB centre by CuA occurs. Both cytochrome a and CuA behave as simple electron transfer centres. The energy-conserving chemistry takes place at the binuclear centre in concert with the four-electron reduction of molecular oxygen.
细胞色素c氧化酶催化的电子向氧的转移，在可溶性酶和膜系统中，都会伴随着双核a3CuB中心的光谱变化，这表明保持三价铁状态的铁的自旋或配体状态发生了转变。另一个血红素基团，即细胞色素a，在稳态期间其光谱特征没有显著变化，但在无氧状态之前一直处于部分还原状态。细胞色素a3在其每种主要稳态形式中都是完全氧化的，在无氧状态下会还原为单一的亚铁物种。虽然细胞色素a通常是双核中心的直接电子供体，但在酶通量发生显著变化的条件下，其氧化还原状态不会改变。因此，可能存在第二条通向双核中心的电子传递途径，可能是通过CuA直接还原双核a3CuB中心的途径。细胞色素a和CuA都表现为简单的电子传递中心。能量守恒化学反应与分子氧的四电子还原反应协同发生在双核中心。
