Regulation of bile acid synthesis. Measurement of cholesterol 7 alpha-hydroxylase activity in rat liver microsomal preparations in the absence of endogenous cholesterol.
Regulation of bile acid synthesis. Measurement of cholesterol 7 alpha-hydroxylase activity in rat liver microsomal preparations in the absence of endogenous cholesterol.
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DOI：
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发表时间：
1981-03
影响因子：
6.5
通讯作者：
S. Shefer;F. Cheng;S. Hauser;A. Batta;G. Salen
中科院分区：
文献类型：
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作者：
S. Shefer;F. Cheng;S. Hauser;A. Batta;G. Salen
建立了一种快速测定肝脏胆固醇7α-羟基酶活性的方法，该方法可以在没有内源性微粒体胆固醇的情况下进行。这种方法包括从大鼠肝脏的微粒体部分制备丙酮粉末，该粉末保留了胆固醇7α-羟基酶的活性，并且几乎不含内源性胆固醇。该酶的活性是在标记的外源胆固醇作为唯一底物来源的情况下测量的，并可以用简单的同位素掺入过程中形成的产物的皮摩尔来表示。确定了最佳测定条件，并建立了丙酮粉末胆固醇7α-羟基酶测定的重复性。将提出的方法与以前使用的双同位素衍生法进行比较，发现对照组大鼠的酶活性相似，两种方法都显示出胆碱胺处理后羟化速率增加，胆酸处理后羟化速率降低。相比之下，丙酮粉末试验没有显示胆固醇喂养过程中胆固醇7α-羟基酶活性的任何变化。这些发现表明，喂饲胆汁酸会影响肝脏中存在的活性胆固醇7α-羟基酶的数量，而喂饲胆固醇则不会。
A rapid procedure was developed to measure hepatic cholesterol 7 alpha-hydroxylase activity in the absence of endogenous microsomal cholesterol. This method involves the preparation of an acetone powder from the microsomal fraction of rat liver that retains its cholesterol 7 alpha-hydroxylase activity and contains virtually no endogenous cholesterol. The enzyme activity is measured in the presence of labeled exogenous cholesterol as the only substrate source, and can be expressed in terms of picomoles of product formed when a simple isotope incorporation procedure is employed. Optimal assay conditions were determined and the reproducibility of the acetone powder cholesterol 7 alpha-hydroxylase assay was established. A comparison of the proposed method with the previously used double isotope derivative procedure showed comparable enzyme activities in control rats and both methods exhibited an increase in the rate of hydroxylation after cholestyramine treatment and a decrease following cholic acid treatment. In contrast, the acetone powder assay did not show any change in cholesterol 7 alpha-hydroxylase activity during cholesterol feeding. These findings suggest that bile acid feeding influences the amount of active cholesterol 7 alpha-hydroxylase present in the liver whereas cholesterol feeding does not.