Cytochrome c oxidase (CcO) is the final oxygen accepting enzyme complex (complex IV) of the mitochondrial respiratory chain. In contrast to the other complexes (I, II, and III), CcO is highly regulated via isoforms for six of its ten nuclear-coded subunits, which are differentially expressed in species, tissues, developmental stages, and cellular oxygen concentrations. Recent publications have claimed that NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4 (NDUFA4), originally identified as subunit of complex I, represents a 14th subunit of CcO. Results on CcO composition in tissues from adult animals and the review of data from recent literature strongly suggest that NDUFA4 is not a 14th subunit of CcO but may represent an assembly factor for CcO or supercomplexes (respirasomes) in mitochondria of growing cells and cancer tissues.

中文翻译：

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哺乳动物 13 亚基细胞色素 c 氧化酶的调节和其他蛋白质的结合：NDUFA4 的作用

细胞色素 c 氧化酶 (CcO) 是线粒体呼吸链的最终氧接受酶复合物（复合物 IV）。与其他复合物（I、II 和 III）相比，CcO 受其 10 个核编码亚基中的 6 个亚基的同工型高度调节，这些亚基在物种、组织、发育阶段和细胞氧浓度中差异表达。最近的出版物声称 NADH 脱氢酶 (泛醌) 1 α 亚复合体 4 (NDUFA4)，最初被确定为复合体 I 的亚基，代表 CcO 的第 14 个亚基。成年动物组织中 CcO 组成的结果和对近期文献数据的回顾强烈表明 NDUFA4 不是 CcO 的第 14 个亚基，但可能代表 CcO 或生长细胞和癌细胞线粒体中超级复合物（呼吸小体）的组装因子。