Norlin M, Wikvall K
Division of Biochemistry, Department of Pharmaceutical Biosciences, University of Uppsala, Box 578, S-751 23 Uppsala, Sweden.
Biochim Biophys Acta. 1998 Feb 23;1390(3):269-81. doi: 10.1016/s0005-2760(97)00193-8.
Microsomal cytochrome P-450 catalyzing the 7alpha-hydroxylation of 27-hydroxycholesterol and dehydroepiandrosterone was partially purified from pig liver. This enzyme fraction also catalyzed 7alpha-hydroxylation of 25-hydroxycholesterol and pregnenolone but did not 7alpha-hydroxylate cholesterol or testosterone. Studies with extrahepatic tissues have suggested the possibility of one common enzyme responsible for the 7alpha-hydroxylation of 27-hydroxycholesterol and dehydroepiandrosterone. A series of experiments was performed to study if there are one or several enzymes 7alpha-hydroxylating these steroids in the liver. The activities towards the two substrates copurified but the ratio between 27-hydroxycholesterol and dehydroepiandrosterone 7alpha-hydroxylation varied considerably in different purification steps and between different preparations. The enzyme inhibitors disulfiram, N-bromosuccinimide, ketoconazole, metyrapone and alpha-naphthoflavone affected the activities in a similar way. Dehydroepiandrosterone inhibited 27-hydroxycholesterol 7alpha-hydroxylation whereas 27-hydroxycholesterol had almost no inhibitory effect on dehydroepiandrosterone 7alpha-hydroxylation. Experiments to examine the nature of inhibition by dehydroepiandrosterone indicated that the two steroids did not compete for the same active site. The results of this study do not rule out the possibility of one single enzyme catalyzing 7alpha-hydroxylation of the two steroids. However, taken together the data suggest that hepatic microsomal 7alpha-hydroxylation of 27-hydroxycholesterol and dehydroepiandrosterone involves at least two, probably closely related, enzymes. (c) 1998 Elsevier Science B. V.
微粒体细胞色素P-450催化27-羟胆固醇和脱氢表雄酮的7α-羟化反应，该酶从猪肝中部分纯化得到。该酶组分还催化25-羟胆固醇和孕烯醇酮的7α-羟化反应，但不催化胆固醇或睾酮的7α-羟化反应。对肝外组织的研究表明，可能存在一种共同的酶负责27-羟胆固醇和脱氢表雄酮的7α-羟化反应。进行了一系列实验以研究肝脏中是否存在一种或几种酶对这些类固醇进行7α-羟化。对两种底物的活性在纯化过程中共纯化，但在不同的纯化步骤和不同的制剂之间，27-羟胆固醇和脱氢表雄酮7α-羟化反应的比率差异很大。酶抑制剂双硫仑、N-溴代琥珀酰亚胺、酮康唑、甲吡酮和α-萘黄酮以类似的方式影响活性。脱氢表雄酮抑制27-羟胆固醇的7α-羟化反应，而27-羟胆固醇对脱氢表雄酮的7α-羟化反应几乎没有抑制作用。研究脱氢表雄酮抑制性质的实验表明，这两种类固醇不竞争相同的活性位点。本研究结果不排除存在一种单一酶催化这两种类固醇7α-羟化反应的可能性。然而，综合这些数据表明，肝脏微粒体中27-羟胆固醇和脱氢表雄酮的7α-羟化反应至少涉及两种可能密切相关的酶。(c)1998爱思唯尔科学出版社B.V.
