Department of Biochemistry, University of Stellenbosch, Stellenbosch 7602, South Africa.
J Steroid Biochem Mol Biol. 2011 Nov;127(3-5):238-47. doi: 10.1016/j.jsbmb.2011.09.001. Epub 2011 Sep 14.
During adrenal steroidogenesis the competition between 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4) isomerase (3βHSD) and cytochrome P450 17α-hydroxylase/17,20 lyase (CYP17A1) for Δ(5) steroid intermediates greatly influences steroidogenic output. Cytochrome-b(5) (Cyt-b(5)), a small electron transfer hemoprotein, known to augment the lyase activity of CYP17A1, has been shown to alter the steroidogenic outcome of this competition. In this study, the influence of Cyt-b(5) on 3βHSD activity was investigated. In COS-1 cells, Cyt-b(5) was shown to significantly increase the activity of both caprine and ovine 3βHSD towards pregnenolone, 17-OH pregnenolone and dehydroepiandrosterone in a substrate and species specific manner. Furthermore, kinetic studies revealed Cyt-b(5) to have no influence on the K(m) values while significantly increasing the V(max) values of ovine 3βHSD for all its respective substrates. In addition, the activity of ovine 3βHSD in microsomal preparations was significantly influenced by the addition of either purified Cyt-b(5) or anti-Cyt-b(5) IgG. The results presented in this study indicate that Cyt-b(5) augments 3βHSD activity and represents the first documentation of such augmentation in any species.
在肾上腺类固醇生成过程中，3β-羟甾脱氢酶/Δ(5)-Δ(4)异构酶（3βHSD）和细胞色素 P450 17α-羟化酶/17,20 裂合酶（CYP17A1）之间对Δ(5)甾体中间产物的竞争极大地影响了甾体生成的输出。细胞色素-b(5)（Cyt-b(5)），一种小的电子转移血红素蛋白，已知可增强 CYP17A1 的裂合酶活性，已被证明改变了这种竞争的甾体生成结果。在这项研究中，研究了 Cyt-b(5)对 3βHSD 活性的影响。在 COS-1 细胞中，Cyt-b(5)显著增加了山羊和绵羊 3βHSD 对孕烯醇酮、17-羟孕烯醇酮和脱氢表雄酮的活性，具有底物和种属特异性。此外，动力学研究表明 Cyt-b(5)对 K(m)值没有影响，而对绵羊 3βHSD 对所有相应底物的 V(max)值有显著影响。此外，添加纯化的 Cyt-b(5)或抗 Cyt-b(5) IgG 显著影响了微粒体制剂中绵羊 3βHSD 的活性。本研究的结果表明，Cyt-b(5)增强了 3βHSD 的活性，这是首次在任何物种中证明这种增强作用。
