FUNCTIONAL ROLES OF UBIQUINONE IN YEAST AND HUMAN CELLS

泛醌是线粒体呼吸系统的重要组成部分， 链 尽管存在于动物的所有器官和组织中， 泛醌的浓度在心脏和骨骼肌中最高。 泛醌的合成和定位通常被认为是有限的 线粒体内膜 然而，最近的一份报告显示， 在大鼠肝脏的内质网上也合成泛醌。 事实上，高尔基 囊泡和溶酶体，与ER密切联系的膜， 比线粒体含有更多的泛醌 功能 泛醌可能在这些其他细胞内区室中起作用， 不清楚 由于泛醌在酵母和其他真核生物中的生物合成， 同样的途径，拟议的研究利用一类呼吸道 酿酒酵母的缺陷突变体，其缺乏 泛醌 突变体分为九个互补组， 用于表征泛醌生物合成的调节， 确定泛醌在非线粒体区室的功能。 3，4-二羟基-5-己异戊二烯苯甲酸酯（DHHB）缺陷的酵母突变体 甲基转移酶，一种调节泛醌合成的酶，将允许 编码这种酶的基因将被克隆。 基因会提供 研究DHHB调节所必需的生化工具 甲基转移酶活性及其在泛醌调节中的作用 生物合成 将构建DHHB甲基转移酶无效突变体， 评估线粒体泛醌合成的缺乏是否影响 泛醌营养缺陷型或在其他细胞器中合成。 病变 将鉴定其它泛醌营养缺陷型突变体。 的酵母突变株 菌株将用作分离人cDNA克隆的载体， 同源性探测策略或通过功能互补。 已经报道了实验性疗法，其中施用 泛醌对心脏病患者线粒体 脑肌病，或与Kearns-Sayre表明，泛醌可能有助于 在预防mevinolin引起的肌肉无力，一个罕见的，但主要的一面， 洛伐他汀降胆固醇治疗效果观察 的机制 哪种泛醌介导这些作用尚不清楚。 拟议的研究 应该增加我们的了解如何泛醌功能，在这些 临床治疗。

Ubiquinone is an essential component of the mitochondrial respiratory chain. Although present in all organs and tissues of animals, the concentration of ubiquinone is highest in heart and skeletal muscle. Ubiquinone synthesis and localization is usually considered to be limited to the inner mitochondrial membrane. However, a recent report has shown that ubiquinone is also synthesized on the ER of rat liver. In fact, Golgi vesicles and lysosomes, membranes in close communication with the ER, contain more ubiquinone on a protein basis that mitochondria. The function ubiquinone might be serving in these other intracellular compartments is not clear. Since ubiquinone biosynthesis in yeast and other eukaryotes have share the same pathway, the proposed studies take advantage of a class of respiratory defective mutants of Saccharomyces cerevisiae that are deficient in ubiquinone. The mutants fall into nine complementation groups, and will be used to characterize the regulation of ubiquinone biosynthesis and to determine the function of ubiquinone in nonmitochondrial compartments. Yeast mutants defective in 3,4-dihydroxy-5-hexaprenyl benzoate (DHHB) methyltransferase, a regulated enzyme of ubiquinone synthesis, will allow the gene encoding this enzyme to be cloned. The gene will provide the biochemical tools necessary to study the regulation of DHHB methyltransferase activity and its role in the regulation of ubiquinone biosynthesis. DHHB methyltransferase null mutants will be constructed to assess whether a lack of mitochondrial ubiquinone synthesis affects ubiquinone auxotrophic or synthesis in other organelles. The lesions in other ubiquinone auxotrophic mutants will be identified. The yeast mutant strains will be used as vehicles for isolating human cDNA clones, either by homology probing strategies or by functional complementation. Experimental therapies have been reported in which administration of ubiquinone to patients with heart disease, mitochondrial encephalomyopathies, or with Kearns-Sayre indicates that ubiquinone may aid in preventing mevinolin induced muscle weakness, a rare but major side effect of hypocholesterolemic therapy with lovastatin. The mechanisms by which ubiquinone mediates these effects is not clear. The proposed studies should increase our understanding of how ubiquinone functions in these clinical therapies.