HEME A AND CYTOCHROME OXIDASE BIOSYNTHESIS

细胞色素氧化酶促进电子从还原态转移 细胞色素c到分子氧，呼吸的终端步骤 线粒体和需氧微生物的链。 in s.酿酒酵母， 这种膜复合物由10种不同的亚基多肽组成 其中三种由线粒体DNA编码。 两个基因 不同的多肽组通过一种酶组装成全酶， 这个复杂的过程需要大约40个核基因的表达。 两个这样的基因的产物，COX10和COX11，最近已经被发现。 与血红素A的合成有关，血红素A是一种辅基， 细胞色素氧化酶所特有的。 该提案的目标之一是 表征COX10和COX11蛋白在法尼基化中的作用 的8-乙烯基和氧化的2-甲基取代基， 卟啉环和筛选其他血红素A突变体。 这些菌株 将用于鉴定血红素的中间体和酶 一种生物合成途径，一种目前几乎一无所知的途径， 礼物 大量的非母系遗传的人类肌病具有 归因于肌肉中细胞色素氧化酶水平的降低 线粒体 尽管有广泛的研究，这些致命的疾病 与基因结构或催化功能的突变有关， 这个呼吸复合体的亚单位。 有理由认为 在某些情况下，酶缺乏可能源于突变， 影响血红素A的生物合成。 为了评估这种可能性，肌肉 将分析来自细胞色素氧化酶缺陷患者的活检 血红素A中间体的积累。 这种方法已经 有助于鉴定酵母cox 11突变体中的新血红素化合物。 其次，将克隆人COX10和COX11的cDNA同源物。 为了便于对可比较的cDNA进行分子分析， 肌病组织 细胞色素氧化酶缺陷型酵母菌株分配到 大约11个互补组是由影响 酶组装途径中的晚期事件。 第三个目标是 我的建议是完成对这组基因的分析，并阐明 由编码蛋白质提供的功能。 这些研究 预计将提供一个遗传信息的蓝图， 控制功能复合物组装的分子机制。

Cytochrome oxidase promotes the transfer of electrons from reduced cytochrome c to molecular oxygen, the terminal step of the respiratory chains of mitochondria and aerobic microorganisms. In S. cerevisiae, this membrane complex is composed of 10 different subunit polypeptides of which three are encoded in mitochondrial DNA. The two genetically distinct groups of polypeptides are assembled into the holoenzyme by an elaborate process that requires the expression of some 40 nuclear genes. The products of two such genes, COX10 and COX11, have recently been implicated to function in the synthesis of heme A, a prosthetic group unique to cytochrome oxidase. One of the goals of this proposal is to characterize the roles of the COX10 and COX11 proteins in farnesylation of the 8-vinyl and oxidation of the 2-methyl substituents of the porphyrin ring and to screen for other heme A mutants. These strains will be used to used to identify the intermediates and enzymes of heme A biosynthesis, a pathway about which virtually nothing is known at present. A substantial number of non-maternally inherited human myopathies have been ascribed to decreased levels of cytochrome oxidase in muscle mitochondria. Despite extensive studies, none of these fatal diseases have been correlated with mutations in the structural or catalytic subunits of this respiratory complex. It is not unreasonable to think that in some cases the enzyme deficiency may stem from mutations affecting heme A biosynthesis. To assess this possibility, muscle biopsies from patients with cytochrome oxidase defects will be analyzed for the accumulation of heme A intermediates. This approach has been helpful in identifying a novel heme compound in a cox11 mutant of yeast. Secondly, the human cDNA homologs of COX10 and COX11 will be cloned in order to facilitate a molecular analysis of the comparable cDNAs from myopathic tissues. The cytochrome oxidase deficient phenotype of yeast strains assigned to approximated 11 complementation groups is elicited by mutations affecting late events in the enzyme assembly pathway. The third goal of this proposal is to complete the analysis of this set of genes and to clarify the functions supplied by the encoded proteins. These studies are anticipated to provide a blueprint of the genetic information and the molecular mechanisms governing assembly of the functional complex.