CHOLESTEROL METABOLISM AND MITOCHONDRIAL CYTOCHROME P450

电子转移蛋白肾上腺素还蛋白（ADX）与游离细胞色素P450结合 (Kd等于0.5微米），但是结合被以下物质的存在大大激活： 胆固醇（kd等于0.02微米）。 黄素蛋白ADX-还原酶结合ADX 甚至具有更高的亲和力，但所有三种蛋白质的三元复合物不 form. 胆固醇侧链裂解动力学表明ADX“穿梭” ADX-还原酶和P450 SCC之间的关系。 反应是通过增加离子激活的 但被Ca离子抑制（ID 50等于50微米）。 11 β-羟基化还利用ADX穿梭，并通过增加的ADX穿梭激活。 离子强度，但在这种情况下，Ca离子是有效的活化剂。 盐可以 通过增强抑制剂的解离来激活侧链切割 氧化的ADX，而对于11 β-羟基化，盐效应仅仅是由于 最小化氧化ADX的稳态水平。 已经开发了一种方法， 溶解肾上腺线粒体，分离内外膜， 最小化胆固醇在膜之间的再分布。 氨鲁米特， 注射到压力大的老鼠体内， 膜通过直接结合P450 SCC。 环己酰亚胺增强总量 线粒体胆固醇和提高水平的外膜。 是 结论是肾上腺ACTH激活的限速事件是转移 胆固醇从线粒体外膜转移到内膜， 这一步与蛋白质合成有关。

The electron-transfer protein adrenodoxin (ADX) binds to free cytochrome P450 (Kd equals 0.5 microns), but binding is greatly activated by the presence of cholesterol (kd equals 0.02 microns). The flavoprotein ADX-reductase binds ADX with even higher affinity, but a ternary complex of all three proteins does not form. Kinetics of cholesterol side chain cleavage indicate that ADX "shuttles" between ADX-reductase and P450 scc. Reaction is activated by increased by ionic strength but is inhibited by Ca ions (ID50 equals 50 microns). 11 beta-hydroxylation also utilizes an ADX-shuttle and is activated by increased ionic strength but in this case Ca ions is a potent activator. Salt may activate side-chain cleavage by enhancing the dissociation of inhibitory oxidized ADX, while for 11 beta-hydroxylation the salt effect is due solely to minimizing steady-state levels of oxidized ADX. A method has been developed for lysing adrenal mitochondria and separating inner and outer membranes, while minimizing cholesterol redistribution between the membranes. Aminoglutethimide, injected into stressed rats, effected an increase in cholesterol in the inner membrane via direct binding to P450scc. Cycloheximde enhanced total mitochondrial cholesterol and enhancing levels in the outer membrane. It is concluded that a rate-limiting event in ACTH-activation of adrenals is transfer of cholesterol from the outer mitochondrial membrane to the inner membrane and that this step is coupled to protein synthesis.