Competition for electron transfer between cytochromes P450scc and P45011 beta in rat adrenal mitochondria.
Competition for electron transfer between cytochromes P450scc and P45011 beta in rat adrenal mitochondria.
复制标题
大鼠肾上腺线粒体中细胞色素 P450scc 和 P45011 β 之间电子转移的竞争。
DOI：
10.1016/0303-7207(93)90023-d
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发表时间：
1993
影响因子：
4.1
通讯作者：
Jefcoate,CR
中科院分区：
文献类型：
--
作者：
Yamazaki,T;McNamara,BC;Jefcoate,CR
大鼠肾上腺线粒体含有大致相同水平的P450scc和P45011β，每一个都被NADPH通过肾上腺素还原酶(ADX-还原酶)和肾上腺素(ADX)还原。在分离线粒体之前，通过激素的激活和体内胆固醇代谢的抑制，结构性胆固醇侧链裂解(SCO)可以增加20倍以上。这种由累积的反应性胆固醇引起的刺激，既不显著影响活性对异柠檬酸(IC)和琥珀酸(SU)浓度的依赖，也不显著影响这些还原剂支持的最大活性比率[3：1]。因此，胆固醇SCC的速率独立地由电子转移和反应性胆固醇的量决定。脱氧皮质酮的羟基化(11个β和18个位置)需要更高水平的每个还原剂，这表明还原剂转移到P45011β的效率较低。在P450scc和P45011β上的反应被低浓度的二元羧酸盐阴离子(富马酸，SU)促进，该反应由IC介导。SU脱氢酶抑制剂的作用和富马酸(一种较差的直接还原剂)的活性表明，NADPH的高产量是苹果酸促进异柠檬酸吸收的结果。只有还原剂的协同作用才足以维持11-脱氧皮质酮(DOC)的最大代谢率，而IC对P450scc完全有效。在P450scc的反应增加(胆固醇负荷或添加20α-羟基胆固醇)降低了P45011β上的DOC代谢，与估计线粒体内NADPH的生成量成反比(1 mM或10 mM SU>；1 mM IC>；10 mM IC)。这些下降被P450scc的抑制所逆转。DOC最大代谢量引起的交叉抑制不那么明显。EGTA/白蛋白处理增强了P450scc和P45011β的活性，可能是通过增加NADPH来减少这种交叉竞争。对还原剂的不同依赖性和交叉竞争的特征与P450scc的电子转移大约三倍有利的分配是一致的，这可能是由于还原的肾上腺素与P450scc的优先相互作用所致。
Rat adrenal mitochondria contain approximately equal levels of P450sccand P45011β, each reduced by NADPH through adrenodoxin reductase (ADX-reductase) and adrenodoxin (ADX). Constitutive cholesterol side-chain cleavage (SCO can be increased over 20-fold through a combination of hormonal activation and inhibition of cholesterol metabolism in vivo prior to isolation of the mitochondria. This stimulation, which results from accumulated reactive cholesterol, does not significantly affect either the dependence of activities on the concentration of isocitrate (IC) and succinate (SU) or the ratio of maximum activities [3:1]supported by these reductants. Thus, the rate of cholesterol SCC is determined independently by electron transfer and the amount of reactive cholesterol. Hydroxylation of deoxycorticosterone (11β and 18 positions) required much higher levels of each reductant, indicating less effective reductant transfer to P45011β. Reactions at P450sccand P45011β, mediated by IC, are enhanced by low concentrations of various dicarboxylates anions (fumarate, SU). The actions of SU dehydrogenase inhibitors and the activity of fumarate, a poor direct reductant, suggest that higher production of NADPH results from malate-enhanced uptake of isocitrate. Only synergistic combinations of reductants are sufficient to sustain maximum rates of 11-deoxycorticosterone (DOC) metabolism, whereas IC is fully effective for P450scc. Increased reaction at P450scc(cholesterol loading or addition of 20α-hydroxycholesterol) decreased simultaneous DOC metabolism at P45011βin inverse proportion to the estimated intramitochondrial generation of NADPH (1 mM or 10 mM SU > 1 mM IC > 10 mM IC). These decreases were reversed by inhibition of P450scc. Crossover inhibition caused by maximum DOC metabolism was less pronounced. EGTA/albumin treatment, which enhanced activities at both P450sccand P45011β, presumably via increased NADPH, diminished this cross-competition. The differential dependence on reductants and the characteristics of crossover competition are consistent with a roughly three-fold more favorable partitioning of electron transfer to P450scc, possibly caused by preferential interaction of reduced adrenodoxin with P450scc.