Cholesterol 7 -hydroxylase in rat liver microsomal preparations.
Subcellular fractions containing microsomes prepared from rat livers homogenized in the absence of EDTA catalysed the oxidation of cholesterol to 7alpha-hydroxycholesterol, 7-oxocholesterol, 7beta-hydroxycholesterol and 5alpha-cholestane-3beta,5,6beta-triol. These reactions required native protein, molecular oxygen and NADPH. It is suggested that these compounds are formed by a peroxidation analogous to the peroxidation of fatty acids catalysed by liver microsomal preparations. Incubations of [4-(14)C]cholesterol with microsomal preparations from rat liver homogenized in the presence of EDTA gave 7alpha-hydroxy[(14)C]cholesterol as the main product. This reaction required molecular oxygen and NADPH, and was inhibited by CO. The mass of 7alpha-hydroxycholesterol formed during the incubation was measured by a double-isotope-derivative dilution procedure. This procedure was used to assay the activity of cholesterol 7alpha-hydroxylase and to measure low concentrations of endogenous 7alpha-hydroxycholesterol in liver.
D000818:Animals; D002247:Carbon Isotopes; D002248:Carbon Monoxide; D002784:Cholesterol / Q000378:metabolism; D002855:Chromatography, Thin Layer; D004492:Edetic Acid; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009249:NADP; D010084:Oxidation-Reduction; D010100:Oxygen; D051381:Rats; D011920:Rats, Inbred WF; D013250:Steroid Hydroxylases / Q000032:analysis*; D014316:Tritium
D002247:Carbon Isotopes; D014316:Tritium; D009249:NADP; D002248:Carbon Monoxide; D002784:Cholesterol; D004492:Edetic Acid; D013250:Steroid Hydroxylases; D010100:Oxygen