McNamara B C, Jefcoate C R
Dept. of Pharmacology, University of Wisconsin Medical School, Madison 53705.
Endocr Res. 1991;17(1-2):185-93. doi: 10.1080/07435809109027196.
The relative effectiveness of succinate and isocitrate in supplying NADPH for cholesterol and deoxycorticosterone (DOC) metabolism by rat adrenal mitochondria has been investigated. As previously seen for cholesterol metabolism, isocitrate supported DOC metabolism at a higher rate than succinate. Maximal rates of DOC metabolism, however, required 10 times more precursor (10mM) than cholesterol metabolism. Addition of DOC to mitochondria inhibited cholesterol metabolism, indicating competition for NADPH between these pathways. Coaddition of these reducing precursors resulted in a substantially greater than additive rate of DOC hydroxylation, but not cholesterol metabolism. The synergistic effect was seen with both 11 beta- and 18 hydroxylation. For both precursors, the synergism was maximal upon addition of only 1 mM of the second precursor. The synergistic effect was far more resistant to added KCN and malonate than succinate supported DOC metabolism, and neither inhibitor affected isocitrate supported DOC metabolism. These results suggest that while cytochromes P450scc and P450(11 beta) use a common supply of NADPH generated by each precursor, there is a pool of NADPH that is only effectively synthesised upon coaddition of precursors and only utilised by cytochrome P450(11 beta). This second NADPH pool may be produced in response to potentiated isocitrate dehydrogenase activity or activation of a different NADPH generating system.
研究了琥珀酸和异柠檬酸在为大鼠肾上腺线粒体胆固醇及脱氧皮质酮（DOC）代谢提供NADPH方面的相对有效性。正如之前在胆固醇代谢中所观察到的，异柠檬酸支持DOC代谢的速率高于琥珀酸。然而，DOC代谢的最大速率所需的前体（10mM）是胆固醇代谢的10倍。向线粒体中添加DOC会抑制胆固醇代谢，表明这些途径之间对NADPH存在竞争。同时添加这些还原前体导致DOC羟化速率显著高于相加速率，但胆固醇代谢并非如此。11β-羟化和18-羟化均出现协同效应。对于两种前体，仅添加1mM的第二种前体时协同作用最大。与琥珀酸支持的DOC代谢相比，协同效应对添加的KCN和丙二酸更具抗性，且两种抑制剂均不影响异柠檬酸支持的DOC代谢。这些结果表明，虽然细胞色素P450scc和P450(11β)使用每种前体产生的共同NADPH供应，但存在一个NADPH池，只有在前体同时添加时才有效合成，且仅被细胞色素P450(11β)利用。这个第二个NADPH池可能是由于异柠檬酸脱氢酶活性增强或不同的NADPH生成系统激活而产生的。
