Cytochrome P-450 of adrenal mitochondria. Spin states as detected by difference spectroscopy.
Cytochrome P-450 of adrenal mitochondria. Spin states as detected by difference spectroscopy.
复制标题
肾上腺线粒体的细胞色素 P-450。
DOI：
10.1016/s0021-9258(19)41352-5
复制
发表时间：
1975
期刊：
影响因子：
--
通讯作者：
C. Jefcoate
中科院分区：
文献类型：
--
作者：
C. Jefcoate
肾上腺线粒体细胞色素 P-450 在胆固醇侧链裂解 (P-450scc) 中发挥作用，与几种类固醇表现出 I 型（lambdamax 385、lambdamin 420 nm）和反向 I 型（lambdamin 385、lambdamax 420 nm）差异光谱。反应的强度和类型取决于特定的类固醇以及胆固醇与完整线粒体中细胞色素的结合程度。 3β-羟基-孕-5-烯-20-酮（孕烯醇酮）诱导的反向 I 型差异谱取决于高自旋胆固醇-细胞色素 P-450scc 复合物的比例。对于大鼠肾上腺线粒体 cholest-5-ene-3beta，20α-二醇（20α-羟基胆固醇）总是诱导较小的反向 I 型反应，并且在细胞色素 P-450scc 几乎不含胆固醇的条件下，甚至产生较小的 I 型反应。细胞色素 P-450scc 上的两个不同类固醇结合位点分别通过对 cholest-5-ene-3beta、25-二醇（25-羟基胆固醇）的缓慢 I 型反应和对随后添加 cholest-5-ene-3beta、20α、22 R-三醇（20α、22R-二羟基胆固醇）的快速 I 型反应来检测。对这些类固醇的光谱响应的相对比例取决于促肾上腺皮质激素 (ACTH) 先前激活肾上腺的程度，因为这种刺激过程改变了线粒体胆固醇与细胞色素 P-450scc 的组合。据推测，细胞色素 P-450scc 上的两个类固醇结合位点通过以下方式与类固醇相互作用：位点 I 结合胆固醇、25-羟基胆固醇和 20α，22R-二羟基胆固醇，形成部分高自旋细胞色素；位点 II 结合孕烯醇酮和 20α-OH 胆固醇，导致细胞色素低自旋。位点 I 和 II 之间的相互作用不是竞争性的，位点 II 的占据确保了低自旋状态，而与位点 I 的占据无关。20α，22R-二羟基胆固醇的第二种相互作用模式稳定了高自旋细胞色素，并与 20α-羟基胆固醇或孕烯醇酮的位点 II 结合竞争。最大高自旋细胞色素的形成遵循 20α, 22R-二羟基胆固醇在两个位点的占据。
Adrenal mitochondrial cytochrome P-450 which functions in cholesterol side chain cleavage (P-450scc) exhibited type I (lambdamax 385, lambdamin 420 nm) and inverse type I (lambdamin 385, lambdamax 420 nm) difference spectra with several steroids. The magnitude and type of response were dependent on the particular steroid and on the extent to which cholesterol was bound to the cytochrome in the intact mitochondrion. the inverse type I difference spectrum induced by 3beta-hydroxy-pregn-5-ene-20-one (pregnenolone) was dependent on the proportion of high spin cholesterol-cytochrome P-450scc complexes. With rat adrenal mitochondria cholest-5-ene-3beta, 20alpha-diol (20alpha-hydroxycholesterol) invariably induced a smaller inverse type I response and, under conditions where cytochrome P-450scc was nearly free of cholesterol, even produced a small type I response. Two distinct steroid binding sites on cytochrome P-450scc were detected by, respectively, the slow type I response to cholest-5-ene-3beta, 25-diol (25-hydroxycholesterol) and the rapid type I response to a subsequent addition of cholest-5-ene-3beta, 20alpha, 22 R-triol (20alpha, 22R-dihydroxycholesterol). The relative proportions of the spectral responses to these steroids were dependent on the previous extent of adrenal activation by adrenocorticotropic hormone (ACTH), because this stimulatory process altered the combination of mitochondrial cholesterol with cytochrome P-450scc. It is proposed that the two steroid binding sites on cytochrome P-450scc interact with steroids in the following way: site I binds cholesterol, 25-hydroxycholesterol, and 20alpha, 22R-dihydroxycholesterol with formation of a partially high spin cytochrome; site II binds both pregnenolone and 20alpha-OH cholesterol resulting in a low spin cytochrome. Interactions between sites I and II are not competitive, and occupancy of site II ensures a low spin state irrespective of the occupancy of site I. A second mode of interaction by 20alpha, 22R-dihydroxycholesterol stabilizes a high spin cytochrome and is competitive with site II binding by 20alpha-hydroxycholesterol or pregnenolone. Formation of a maximally high spin cytochrome follows occupancy by 20alpha, 22R-dihydroxycholesterol at both sites.