Moustafa A M, Koritz S B
Eur J Biochem. 1977 Aug 15;78(1):231-8. doi: 10.1111/j.1432-1033.1977.tb11734.x.
The Ca2+ stimulation and ADP inhibition of the steroid 11beta-hydroxylation enzyme system in adrenal mitochondria have been investigated. The Ca2+-stimulation is competitively inhibited by Sr2+. Nucleoside monophosphates were not inhibitory and among the nucleoside diphosphates and triphosphates only ADP, CDP and ATP were inhibitory with ADP being more inhibitory than the other nucleotides. None of the non-inhibitory nucleotides could reverse the ADP inhibition. ADP appears to inhibit the Ca2+-stimulation since the activity in the absence of Ca2+ was not inhibited by ADP. Ca2% and ADP did not affect the binding of deoxycorticosterone to the mitochondrial preparation. Ca2+ stimulated the reduction of cytochrome P-450 by NADPH and this was inhibited by ADP. These effects were independent of the presence of deoxycorticosterone. Neither Ca2+ nor ADP affected the reduction of adrenodoxin by NADPH. The inhibition by ADP with respect to Ca2+ or to deoxycorticosterone is non-competitive. The Ca2+ stimulation with respect to deoxycorticosterone is uncompetitive. Preincubation of the mitochondrial preparation with Ca2+ decreases the inhibition by ADP and preincubation with ADP increases its inhibitory effects. These data have been interpreted to indicate that Ca2+ and ADP influence the relationship between adrenodoxin and cytochrome P-450 so that a complex of increased activity in the reduction of cytochrome P-450 is formed in the presence of Ca2+ and a less active complex is formed in the presence of Ca2+ plus ADP.
对肾上腺线粒体中甾体11β - 羟化酶系统的钙离子刺激作用和二磷酸腺苷（ADP）抑制作用进行了研究。钙离子刺激作用受到锶离子（Sr2 +）的竞争性抑制。核苷单磷酸没有抑制作用，在核苷二磷酸和三磷酸中，只有ADP、二磷酸胞苷（CDP）和三磷酸腺苷（ATP）具有抑制作用，其中ADP的抑制作用比其他核苷酸更强。没有一种非抑制性核苷酸能够逆转ADP的抑制作用。ADP似乎抑制了钙离子的刺激作用，因为在没有钙离子的情况下，其活性不受ADP抑制。钙离子和ADP不影响脱氧皮质酮与线粒体制剂的结合。钙离子刺激还原型辅酶Ⅱ（NADPH）对细胞色素P - 450的还原作用，而这一作用受到ADP的抑制。这些效应与脱氧皮质酮的存在无关。钙离子和ADP都不影响NADPH对肾上腺铁氧化还原蛋白的还原作用。ADP对钙离子或脱氧皮质酮的抑制作用是非竞争性的。钙离子对脱氧皮质酮的刺激作用是反竞争性的。线粒体制剂与钙离子预孵育会降低ADP的抑制作用，而与ADP预孵育会增强其抑制作用。这些数据被解释为表明钙离子和ADP影响肾上腺铁氧化还原蛋白与细胞色素P - 450之间的关系，从而在有钙离子存在时形成细胞色素P - 450还原活性增强的复合物，而在有钙离子和ADP存在时形成活性较低的复合物。
