Cooper C E, Nicholls P, Freedman J A
Division of Biomolecular Sciences, King's College London, U.K.
Biochem Cell Biol. 1991 Sep;69(9):586-607. doi: 10.1139/o91-089.
Mitochondrial cytochrome c oxidase and its bacterial homologs catalyze electron transfer and proton translocation reactions across membranes. The eukaryotic enzyme complex consists of a large number of polypeptide subunits. Three of the subunits (I, II, and III) are mitochondrially encoded while the remaining 6 (yeast) to 10 (bovine) are nuclear encoded. Antibody and chemical-labelling experiments suggest that subunits I-III and most (but not all) of the nuclear-encoded subunits span the inner mitochondrial membrane. Subunits I and II are the catalytic core of the enzyme. Subunit I contains haem a, haem a3 and CuB, while subunit II contains CuA and the cytochrome c binding site. Subunit III and most of the nuclear subunits are essential for the assembly of a functional catalytic enzyme. Some nuclear subunits are present as isozymes, although little functional difference has yet been detected between enzyme complexes composed of different isozymes. Therefore, any additional role attributed to the nuclear-encoded subunits beyond that of enzyme assembly must be tentative. We suggest that enough evidence exists to support the idea that modification of the larger nuclear subunits (IV, V, and possibly VI) can effect enzyme turnover in vitro. Whether this is a physiological control mechanism remains to be seen.
线粒体细胞色素c氧化酶及其细菌同源物催化跨膜电子转移和质子转运反应。真核酶复合物由大量多肽亚基组成。其中三个亚基（I、II和III）由线粒体编码，其余6个（酵母）至10个（牛）由核编码。抗体和化学标记实验表明，亚基I-III以及大多数（但不是全部）核编码亚基跨越线粒体内膜。亚基I和II是该酶的催化核心。亚基I含有血红素a、血红素a3和CuB，而亚基II含有CuA和细胞色素c结合位点。亚基III和大多数核亚基对于功能性催化酶的组装至关重要。一些核亚基以同工酶形式存在，尽管由不同同工酶组成的酶复合物之间尚未检测到明显的功能差异。因此，除了酶组装之外，赋予核编码亚基的任何其他作用都必须是试探性的。我们认为有足够的证据支持这样的观点，即较大的核亚基（IV、V，可能还有VI）的修饰可以在体外影响酶的周转。这是否是一种生理控制机制还有待观察。
