HEME A AND CYTOCHROME OXIDASE BIOSYNTHESIS

细胞色素氧化酶促进还原的电子转移 从细胞色素c到分子氧，这是呼吸的最后一步 线粒体链和好氧微生物。在酿酒酵母中， 该膜复合体由10种不同的亚基多肽组成 其中三个编码在线粒体DNA中。这两个人的基因 不同的多肽基团通过一种 复杂的过程需要大约40个核基因的表达。 两个这样的基因COX10和COX11的产物最近被 与血红素A的合成有关，这是一种人工基团 细胞色素氧化酶所特有的。这项提案的目标之一是 研究COX10和COX11蛋白在法尼化反应中的作用 的8-乙烯基和2-甲基取代基的氧化 并筛选其他血红素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，一种几乎一无所知的途径 现在时。 相当数量的非母系遗传性人类肌病 归因于肌肉中细胞色素氧化酶水平的降低 线粒体。尽管进行了广泛的研究，但这些致命的疾病中 与结构或催化的突变有关 呼吸复合体的亚单位。认为这并不是没有道理的 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 细胞色素氧化酶缺陷患者的活组织检查将被分析 用于血红素A中间体的积累。这一方法一直是 有助于在酵母的cox11突变体中鉴定一种新的血红素化合物。 其次，将克隆人COX10和COX11的同源基因 为了便于对可比的cDNA进行分子分析 肌病组织。 酵母菌的细胞色素氧化酶缺陷表型 大约11个互补基团是由影响 酶组装途径中的晚期事件。这方面的第三个目标 建议是完成对这组基因的分析并澄清 由编码的蛋白质提供的功能。这些研究是 预计将提供遗传信息的蓝图和 控制功能复合体组装的分子机制。

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.