Colby H D, Eacho P I
J Steroid Biochem. 1985 Oct;23(4):477-82. doi: 10.1016/0022-4731(85)90195-5.
Previous investigations have demonstrated that cells isolated from the outer zone (zona fasciculata + zona glomerulosa) of the guinea-pig adrenal cortex produce far more cortisol than those from the inner zone (zona reticularis). Studies were carried out to compare mitochondrial steroid metabolism in the two zones. Protein and cytochrome P-450 concentrations were similar in outer and inner zone mitochondria. However, the rate of 11 beta-hydroxylation was significantly greater in the outer zone despite the fact that substrates for 11 beta-hydroxylation (11-deoxycortisol, 11-deoxycorticosterone) produced larger type I spectral changes in inner zone mitochondria. The apparent affinities of 11-deoxycortisol and 11-deoxycorticosterone for mitochondrial cytochrome(s) P-450 were similar in the two zones. In both inner and outer zone mitochondria, 11 beta-hydroxylation was inhibited by metyrapone but unaffected by aminoglutethimide. Cholesterol sidechain cleavage activity, measured as the rate of conversion of endogenous cholesterol to pregnenolone, was far greater in outer than inner zone mitochondria. Addition of exogenous cholesterol or 25-hydroxycholesterol to the mitochondrial preparations did not affect pregnenolone production in either zone. Addition of pregnenolone to outer zone mitochondria produced a reverse type I spectral change (delta A 420-390 nm), suggesting displacement of endogenous cholesterol from cytochrome P-450. In inner zone mitochondria, pregnenolone induced a difference spectrum (delta A 425-410 nm) similar to the reduced vs oxidized cytochrome b5 spectrum. A b5-like cytochrome was found to be present in the mitochondrial preparations. Prior reduction of the cytochrome with NADH eliminated the pregnenolone-induced spectral change in inner zone mitochondria but had no effect in outer zone preparations. The results suggest that differences in mitochondrial steroid metabolism between the inner and outer adrenocortical zones account in part for the differences in cortisol production by cells in each zone.
先前的研究表明，从豚鼠肾上腺皮质外层（束状带+球状带）分离的细胞产生的皮质醇比内层（网状带）的细胞多得多。开展了多项研究以比较这两个区域中线粒体类固醇代谢情况。外层和内层线粒体中的蛋白质和细胞色素P-450浓度相似。然而，尽管11β-羟化作用的底物（11-脱氧皮质醇、11-脱氧皮质酮）在内层线粒体中产生更大的I型光谱变化，但外层的11β-羟化速率明显更高。11-脱氧皮质醇和11-脱氧皮质酮对线粒体细胞色素P-450的表观亲和力在两个区域中相似。在内外层线粒体中,11β-羟化作用均被美替拉酮抑制，但不受氨鲁米特影响。以内源性胆固醇转化为孕烯醇酮的速率来衡量，胆固醇侧链裂解活性在外层线粒体中比内层线粒体中高得多。向线粒体制剂中添加外源性胆固醇或25-羟胆固醇对两个区域中孕烯醇酮的产生均无影响。向外层线粒体中添加孕烯醇酮会产生反向I型光谱变化（ΔA 420 - 390 nm），表明内源性胆固醇从细胞色素P-450上被置换。在内层线粒体中，孕烯醇酮诱导出一种差异光谱（ΔA 425 - 410 nm），类似于还原型与氧化型细胞色素b5光谱。发现线粒体制剂中存在一种类似b5的细胞色素。先用NADH还原该细胞色素可消除孕烯醇酮在内层线粒体中诱导的光谱变化，但在外层制剂中无此作用。结果表明，肾上腺皮质内外层之间线粒体类固醇代谢的差异部分解释了每个区域中细胞产生皮质醇的差异。
