ROLE OF PEROXISOMES IN CHOLESTEROL OXIDATION

总的目标是扩展我们正在进行的工作过氧化物酶体胆汁酸 合成并表征过氧化物酶体HMG-CoA还原酶。 我们有 最近表明，大鼠肝脏过氧化物酶体能够代谢 26-羟基胆固醇转化为C-24胆汁酸，3 β-羟基-5-胆烯酸。 我们刚刚也证明了过氧化物酶体含有羟化酶 对3 α，7 α，12 α，-三羟基-5 β-胆甾烷有活性， 胆汁酸合成中26-羟基化的主要底物。 通过使用 细胞分级方法，我们最近证实了免疫电子 Keller等人的显微镜数据表明，大鼠肝脏过氧化物酶体含有HMG-CoA 还原酶，胆固醇生物合成中的限速酶，和 已经扩展了调查结果，建议对 微粒体和过氧化物酶体酶。 研究包括确定过氧化物酶体脂肪酸氧化的酶 负责胆固醇的过氧化物酶体侧链氧化。 我们 还将描述过氧化物酶体羟化酶的特征， 细胞色素P-450活性，羟基化位置，最佳辅因子 要求和底物特异性。 其他的研究是针对 对过氧化物酶体胆汁酸的意义的调查 体内合成。 过氧化物酶体HMG-CoA还原酶的研究将包括 确定酶的分子量以及它是否可以 通过磷酸化/去磷酸化机制调节。 最后我们 将检测是否存在其他过氧化物酶体酶， 参与HMG-CoA、胆固醇和多萜醇的生物合成。 胆汁酸的代谢以及胆固醇的调节 合成对于我们理解胆固醇具有根本重要性 代谢、动脉疾病和胆结石形成。 此外还有 是过氧化物酶体缺乏性疾病，如Zellweger综合征、Retsum综合征、 疾病和肌腱黄瘤病，所有这些都导致死亡， 包括胆固醇和脂肪酸异常 新陈代谢. 因此，阐明过氧化物酶体在胆固醇中的作用 氧化将导致对脂质相关疾病的更好理解 和过氧化物酶体代谢紊乱。

The overall aim is to extend our ongoing work on peroxisomal bile acid synthesis and to characterize the peroxisomal HMG-CoA reductase. We have recently shown that rat liver peroxisomes are capable of metabolizing 26-hydroxycholesterol to a C-24 bile acid, 3Beta-hydroxy-5-cholenoic acid. We have also just demonstrated that peroxisomes contain a hydroxylase active toward 3Alpha, 7Alpha, 12Alpha,-trihydroxy-5Beta-cholestane, the major substrate of 26-hydroxylation in bile acid synthesis. By the use of cell fractionation methods, we have recently confirmed the immunoelectron microscopy data of Keller et al. that rat liver peroxisomes contain HMG-CoA reductase, the rate-limiting enzyme in the biosynthesis of cholesterol, and have extended the findings to suggest independent regulation of the microsomal and peroxisomal enzymes. Studies include determining if enzymes of peroxisomal fatty acid oxidation are responsible for peroxisomal side-chain oxidation of cholesterol. We will also characterize the peroxisomal hydroxylase with regards to cytochrome P-450 activity, the position of hydroxylation, optimal co-factor requirements, and substrate specificity. Other studies are directed towards the investigation of the significance of peroxisomal bile acid synthesis in vivo. Studies on peroxisomal HMG-CoA reductase will include determining the molecular weight of the enzyme and whether it can be regulated via a phosphorylation/dephosphorylation mechanism. Finally, we will test for the presence of other peroxisomal enzymes which may participate in the biosynthesis of HMG-CoA, cholesterol, and dolichol. The metabolism of bile acids as well as the regulation of cholesterol synthesis is of fundamental importance to our understanding of cholesterol metabolism, arterial disease, and gallstone formation. In addition, there are peroxisomal deficiency diseases such as Zellweger's Syndrome, Retsum's disease, and cerebrotendinous xanthomatosis, all of which cause death in early infancy and include abnormalities in cholesterol and fatty acid metabolism. Thus, clarification of the role of peroxisomes in cholesterol oxidation will lead to a greater understanding of lipid-related diseases and peroxisomal metabolic disorders.