Ono T, Ozasa S, Hasegawa F, Imai Y
Biochim Biophys Acta. 1977 Mar 25;486(3):401-7.
Microsomal squalene epoxidase has previously been solubilized with Triton X-100 and resolved into fractions, FA and FB, by DEAE-cellulose chromatography (Ono T. and Bloch K (1975) J biol. Chem. 250, 1571-1579). It has now been found that FB is identical with NADPH-cytochrome c reductase (denoted FPT, EC 1.6.2.3). Although both NADPH and NADH served as electron donors, the former was preferred for squalene epoxidase activity in the reconstituted system of FA and FB. FB is characterized by its ability to reduce cytochrome c by NADPH. In place of FB, partially purified FPT was tested for its ability to support squalene epoxidation in the presence of FA. A stepwise purification of the deoxycholate-solubilized FPT yielded an increase in specific FPT activity with a parallel increase in squalene epoxidase activity. Bromelain-solubilized FPT was less effective. Rabbit antisera preparations to the purified FPT solubilized with trypsin were shown to inhibit concomitantly FPT activity and squalene epoxidase activity. These observations support the concept that squalene epoxidation is primarily mediated via a flavoprotein, NADPH-cytochrome c reductase, and a terminal oxidase, squalene epoxidase, which is distinct from cytochrome P-450.
微粒体角鲨烯环氧酶先前已用Triton X - 100溶解，并通过DEAE - 纤维素色谱法分离成FA和FB组分（Ono T.和Bloch K（1975年）《生物化学杂志》250，1571 - 1579）。现已发现FB与NADPH - 细胞色素c还原酶（称为FPT，EC 1.6.2.3）相同。虽然NADPH和NADH都可作为电子供体，但在FA和FB的重组体系中，角鲨烯环氧酶活性更倾向于前者。FB的特征在于其能够通过NADPH还原细胞色素c。用部分纯化的FPT代替FB，测试其在FA存在下支持角鲨烯环氧化的能力。对脱氧胆酸盐溶解的FPT进行逐步纯化，导致FPT比活性增加，同时角鲨烯环氧酶活性也平行增加。菠萝蛋白酶溶解的FPT效果较差。用胰蛋白酶溶解的纯化FPT制备的兔抗血清显示可同时抑制FPT活性和角鲨烯环氧酶活性。这些观察结果支持了这样一种概念，即角鲨烯环氧化主要通过一种黄素蛋白NADPH - 细胞色素c还原酶和一种末端氧化酶角鲨烯环氧酶介导，角鲨烯环氧酶与细胞色素P - 450不同。
