Murray M
Department of Medicine, University of Sydney, Westmead Hospital, NSW, Australia.
J Steroid Biochem Mol Biol. 1991 May;38(5):611-9. doi: 10.1016/0960-0760(91)90320-5.
The metabolism of testosterone (TEST), androstenedione (AD) and progesterone (PROG) was assessed in hepatic microsomal fractions from male sheep. Rates of total hydroxylation of each steroid were lower in sheep liver than in microsomes isolated from untreated male rat, guinea pig or human liver, 6 beta-Hydroxylation was the most important pathway of biotransformation of each of the three steroids (0.80, 0.89 and 0.43 nmol/min/mg protein for TEST, AD and PROG, respectively). Significant minor metabolites from TEST were the 2 beta-, 15 beta- and 15 alpha-alcohols (0.19, 0.22 and 0.17 nmol/min/mg microsomal protein, respectively). Apart from the 6 beta-hydroxysteroid, only the 21-hydroxy derivative was formed from PROG at a significant rate (0.27 nmol/min/mg protein). The 6 beta-alcohol was the only metabolite formed from AD at a rate greater than 0.1 nmol/min/mg protein. Antisera raised in rabbits to several rat hepatic microsomal P450s were assessed for their capacity to modulate sheep microsomal TEST hydroxylation. Anti-P450 IIIA isolated from phenobarbital-induced rat liver effectively inhibited TEST hydroxylation at the 2 beta-, 6 beta-, 15 alpha- and 15 beta-positions (by 31-56% when incubated with microsomes at a ratio of 5 mg IgG/mg protein). IgG raised against rat P450 IIC11 and IIB1 inhibited the formation of some of the minor hydroxysteroid metabolites but did not decrease the rate of TEST 6 beta-hydroxylation. Western immunoblot analysis confirmed the cross-reactivity of anti-rat P450 IIIA with an antigen in sheep hepatic microsomes; anti-IIC11 and anti-IIB1 exhibited only weak immunoreactivity with proteins in these fractions. Considered together, the present findings indicate that, as is the case in many mammalian species, 6 beta-hydroxylation is the principal steroid biotransformation pathway of male sheep liver. Evidence from immunoinhibition and Western immunoblot experiments strongly implicate the involvement of a P450 from the IIIA subfamily in ovine steroid 6 beta-hydroxylation.
在雄性绵羊肝脏微粒体组分中评估了睾酮（TEST）、雄烯二酮（AD）和孕酮（PROG）的代谢情况。绵羊肝脏中每种甾体的总羟基化速率低于从未经处理的雄性大鼠、豚鼠或人类肝脏分离的微粒体。6β-羟基化是这三种甾体生物转化的最重要途径（TEST、AD和PROG分别为0.80、0.89和0.43 nmol/分钟/毫克蛋白质）。TEST产生的重要次要代谢产物是2β-、15β-和15α-醇（分别为0.19、0.22和0.17 nmol/分钟/毫克微粒体蛋白质）。除了6β-羟基甾体外，PROG仅以显著速率形成21-羟基衍生物（0.27 nmol/分钟/毫克蛋白质）。6β-醇是AD形成的唯一速率大于0.1 nmol/分钟/毫克蛋白质的代谢产物。评估了用几种大鼠肝脏微粒体P450免疫家兔产生的抗血清调节绵羊微粒体TEST羟基化的能力。从苯巴比妥诱导的大鼠肝脏中分离的抗P450 IIIA有效抑制了TEST在2β-、6β-、15α-和15β-位的羟基化（当以5毫克IgG/毫克蛋白质的比例与微粒体孵育时，抑制率为31%-56%）。针对大鼠P450 IIC11和IIB1产生的IgG抑制了一些次要羟基甾体代谢产物的形成，但未降低TEST 6β-羟基化的速率。蛋白质免疫印迹分析证实抗大鼠P450 IIIA与绵羊肝脏微粒体中的一种抗原具有交叉反应性；抗IIC11和抗IIB1与这些组分中的蛋白质仅表现出微弱的免疫反应性。综合考虑，目前的研究结果表明，与许多哺乳动物物种一样，6β-羟基化是雄性绵羊肝脏甾体生物转化的主要途径。免疫抑制和蛋白质免疫印迹实验的证据强烈表明IIIA亚家族的一种P450参与了绵羊甾体6β-羟基化。
