7-脱氢胆固醇的生物转化及关于双键还原的评论
The biological conversion of 7-dehydrocholesterol into cholesterol and comments on the reduction of double bonds.
作者信息
Wilton D C, Munday K A, Skinner S J, Akhtar M
出版信息
Biochem J. 1968 Feb;106(4):803-10. doi: 10.1042/bj1060803.
It is shown that the 7-dehydrocholesterol reductase-catalysed conversion of 7-dehydrocholesterol into cholesterol (II), with a 105000g microsomal pellet of rat liver in the presence of [4-(3)H(2)]NADPH, results in the transfer of radioactivity to the 7alpha-position of cholesterol. When the conversion is carried out in the presence of tritiated water the label is introduced exclusively at the 8beta-position. However, when the conversion of 7-dehydrocholesterol into cholesterol is performed with a 500g supernatant of rat liver homogenate the radioactivity is incorporated at both the 7alpha- and the 8beta-position. Evidence is provided for the presence of an enzyme system in the 500g supernatant that catalyses an equilibration of hydrogen atoms between those at the 4-position of NADPH and those of water. The work with stereospecifically labelled cofactors shows that both the equilibrating system and the 7-dehydrocholesterol reductase utilize the 4B-hydrogen atom of NADPH. In the light of these results a mechanism for the reduction of carbon-carbon double bonds is discussed.
结果表明，在[4-(3)H(2)]NADPH存在下，用大鼠肝脏105000g微粒体沉淀进行7-脱氢胆固醇还原酶催化的7-脱氢胆固醇向胆固醇（II）的转化时，放射性转移至胆固醇的7α位。当在氚水存在下进行转化时，标记仅引入到8β位。然而，当用大鼠肝脏匀浆500g上清液进行7-脱氢胆固醇向胆固醇的转化时，放射性同时掺入7α位和8β位。有证据表明500g上清液中存在一种酶系统，该系统催化NADPH 4位的氢原子与水中的氢原子之间的氢原子平衡。使用立体特异性标记辅因子的研究表明，平衡系统和7-脱氢胆固醇还原酶均利用NADPH的4B-氢原子。根据这些结果，讨论了碳-碳双键还原的机制。
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