Mitropoulos K A, Balasubramaniam S
Biochem J. 1972 Jun;128(1):1-9. doi: 10.1042/bj1280001.
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.
在无乙二胺四乙酸（EDTA）的情况下将大鼠肝脏匀浆制备的含微粒体的亚细胞组分催化胆固醇氧化生成7α-羟基胆固醇、7-氧代胆固醇、7β-羟基胆固醇和5α-胆甾烷-3β,5,6β-三醇。这些反应需要天然蛋白质、分子氧和烟酰胺腺嘌呤二核苷酸磷酸（NADPH）。有人提出这些化合物是通过类似于肝脏微粒体制剂催化的脂肪酸过氧化作用的过氧化反应形成的。在有EDTA存在的情况下将大鼠肝脏匀浆制备的微粒体与[4-(14)C]胆固醇一起温育，以7α-羟基[(14)C]胆固醇作为主要产物。该反应需要分子氧和NADPH，并被一氧化碳（CO）抑制。温育过程中形成的7α-羟基胆固醇的量通过双同位素衍生稀释法测定。该方法用于测定胆固醇7α-羟化酶的活性以及测量肝脏中低浓度的内源性7α-羟基胆固醇。
