Hall P F
Adv Exp Med Biol. 1976;74:303-13. doi: 10.1007/978-1-4684-3270-1_23.
A cytochrome P-450 from bovine adrenocortical mitochondria has been purified to near homogeneity. The protein catalyzes side-chain cleavage of cholesterol (cholesterol leads to pregnenolone) but neither 11beta- nor 18-hydroxylation. It consists of 16 subunits of two species (MW 52,000) and contains 8 heme groups. The enzyme has been used to determine the stoichiometry of side-chain cleavage with the following results: (TPNH and O2 consumed/mole of cleavage), cholesterol 3:3:1, 20S-hydroxycholesterol 2:2:1 and 20S,22R-dihydroxycholesterol 1:1:1. These findings support the occurrence of the proposed pathway for the side-chain cleavage of cholesterol. Cleavage of the diol is inhibited by CO and shows a characteristic P-450 photochemical action spectrum. Evidently the diol is cleaved in a typical monoxygenase reaction. The active form of the enzyme contains 16 subunits (protein 16); forms consisting of 8 (protein 8) and 4 (protein 4) subunits can be isolated and are enzymatically active only by prior conversion to protein 16.
一种来自牛肾上腺皮质线粒体的细胞色素P-450已被纯化至接近均一。该蛋白质催化胆固醇的侧链裂解（胆固醇生成孕烯醇酮），但不催化11β-或18-羟基化。它由两种类型的16个亚基（分子量52,000）组成，并含有8个血红素基团。该酶已被用于确定侧链裂解的化学计量关系，结果如下：（每摩尔裂解消耗的TPNH和O2），胆固醇为3:3:1，20S-羟基胆固醇为2:2:1，20S,22R-二羟基胆固醇为1:1:1。这些发现支持了所提出的胆固醇侧链裂解途径的存在。二醇的裂解受到CO的抑制，并显示出特征性的P-450光化学作用光谱。显然，二醇是在典型的单加氧酶反应中被裂解的。该酶的活性形式含有16个亚基（蛋白质16）；由8个（蛋白质8）和4个（蛋白质4）亚基组成的形式可以被分离出来，并且只有在预先转化为蛋白质16后才具有酶活性。
