title: The biological conversion of 7-dehydrocholesterol into cholesterol and comments on the reduction of double bonds.
abstract: 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.
mesh_terms: D000818:Animals; D002784:Cholesterol / Q000096:biosynthesis*; D002855:Chromatography, Thin Layer; D008099:Liver / Q000201:enzymology; D008297:Male; D008861:Microsomes / Q000201:enzymology; D009249:NADP / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism*; D051381:Rats; D013261:Sterols / Q000378:metabolism*; D014316:Tritium
chemical_list: D013261:Sterols; D014316:Tritium; D009249:NADP; D002784:Cholesterol; D010088:Oxidoreductases