Kido T, Yamakura F, Kimura T
Biochim Biophys Acta. 1981 Dec 23;666(3):370-81. doi: 10.1016/0005-2760(81)90296-4.
We have studied the cholesterol-binding reaction with purified steroid-free cytochrome P-450scc. By mixing an aqueous solution of cholesterol-, pregnenolone- and progesterone-free cytochrome with cholesterol-containing liposomes, the low to high spin conversion of the hemoprotein was observed spectrophotometrically and by electron spin resonance spectroscopy. When the binding rates were compared at a fixed molar heme: cholesterol ratio of 1 : 1, 20 mol% cholesterol-dioleoylglycerophosphocholine liposomes react with the cytochrome at a faster rate than 50 mol% cholesterol-dimyristoylglycerophosphocholine liposomes, indicating that the availability of cholesterol molecules in an unsaturated membrane is better than in a saturated membrane. When the number of cholesterol-dioleoylglycerophosphocholine liposomes was increased, the cholesterol-binding rates increased markedly. These results imply that the collision of the liposomes with the soluble hemoprotein molecules plays an important role in the binding reaction under our experimental conditions. The binding reaction was found to be temperature-dependent with a refractive temperature at near 20 degrees C. From the comparison of the binding abilities among cholesterol derivatives tested, wer conclude that the alpha-face of the A-B transfused rings and the portion of the hydrocarbon side-chain of cholesterol are important for the binding. Additionally, polar derivatives had faster rates than non-polar steroids in structurally homologous series.
我们用纯化的无甾体细胞色素P-450scc研究了胆固醇结合反应。通过将不含胆固醇、孕烯醇酮和孕酮的细胞色素水溶液与含胆固醇的脂质体混合，用分光光度法和电子自旋共振光谱法观察到了血蛋白从低自旋到高自旋的转变。当在固定的血红素：胆固醇摩尔比为1:1的条件下比较结合速率时，20mol%胆固醇-二油酰甘油磷酸胆碱脂质体与细胞色素的反应速率比50mol%胆固醇-二肉豆蔻酰甘油磷酸胆碱脂质体快，这表明不饱和膜中胆固醇分子的可利用性优于饱和膜。当增加胆固醇-二油酰甘油磷酸胆碱脂质体的数量时，胆固醇结合速率显著增加。这些结果表明，在我们的实验条件下，脂质体与可溶性血蛋白分子的碰撞在结合反应中起重要作用。发现结合反应与温度有关，转折温度接近20℃。通过比较所测试的胆固醇衍生物的结合能力，我们得出结论，胆固醇A-B反式稠合环的α面和烃侧链部分对结合很重要。此外，在结构同源系列中，极性衍生物的反应速率比非极性甾体快。
