26-Hydroxylation of C27-steroids by soluble liver mitochondrial cytochrome P-450.
26-Hydroxylation of C27-steroids by soluble liver mitochondrial cytochrome P-450.
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可溶性肝线粒体细胞色素 P-450 对 C27-类固醇进行 26-羟基化。
DOI：
10.1016/s0021-9258(18)50390-2
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发表时间：
1979
期刊：
影响因子：
--
通讯作者：
J. Gustafsson
中科院分区：
文献类型：
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作者：
J. Pedersen;I. Björkhem;J. Gustafsson
对先前从大鼠肝线粒体中分离的细胞色素 P-450 制剂的酶学特性进行了研究（Pedersen, JI, Oftehro, H., and VPnng&rd, T.(1977) Biochem. Biophys. Res. Commun. 76, 666-673; Pedersen, JI (1978) FEBS L&t. 85, 35-39)进行。研究发现用苯巴比妥治疗大鼠可增加从肝线粒体中分离出的细胞色素 P-450 的数量和比含量。通过由细胞色素 P-450 制剂、肾上腺氧还蛋白、肾上腺氧还蛋白还原酶和 NADPH 生成系统组成的重建系统，发现几种被认为是胆汁酸形成中间体的 CzT-类固醇在 26 位被羟基化。 5-胆甾烯-3P、7a-二醇和7a-羟基-4-胆甾烯-3-酮的羟基化率最高，其次是S-胆甾烷-3a、7a、12a-三醇和5/3-胆甾烷-3a、7a-二醇。胆固醇的羟基化速率约为其他底物的十分之一。与分离的线粒体相比，重组系统的转化率几乎高出 1 个数量级，并且表观 K,, 低约 1 个数量级，表明类固醇转移到线粒体中可能是限速步骤。线粒体重建系统的周转数（每分钟每摩尔细胞色素 P-450 形成的产物摩尔数）比先前研究的重建微粒体系统高约 2 个数量级。因此，线粒体细胞色素 P-450 比微粒体细胞色素 P-450 具有更高的 26-羟基化潜力。
A study of the enzymatic properties of a cytochrome P-450 preparation previously isolated from rat liver mitochondria(Pedersen, JI, Oftehro, H., and VPnng&rd, T.(1977) Biochem. Biophys. Res. Commun. 76, 666-673; Pedersen, JI (1978) FEBS L&t. 85, 35-39) has been undertaken. Treatment of rats with phenobarbital was found to increase both the amount and the specific content of cytochrome P-450 isolated from the liver mitochondria.With a reconstituted system consisting of the cytochrome P-450 preparation, adrenodoxin, adrenodoxin reductase, and a NADPH-generating system, several CzT-steroids considered to be intermediates in the formation of bile acids were found to be hydroxylated in the 26-position. The rate of hydroxylation was highest with 5-cholestene-3P, 7a-diol and 7a-hydroxy-4-cholestene-3-one followed by S~-cholestane-3a, 7a, l2a-triol and 5/3-cholestane-3a, 7a-diol. The rate of hydroxylation of cholesterol was of the order of one-tenth the rate of the other substrates. The rate of conversion was almost 1 magnitude higher, and the apparent K,,, about 1 magnitude lower with the reconstituted system than with isolated mitochondria, indicating that transfer of steroids into the mitochondria might be the rate-limiting step. The turnover number (moles of product formed per mol of cytochrome P-450 per min) was about 2 magnitudes higher with the mitochondrial reconstituted system than with previously studied reconstituted microsomal systems. Thus the mitochondrial cytochrome P-450 has much higher potential for 26-hydroxylation than microsomal cytochrome P-450.