Regulation of cholesterol 7 alpha-hydroxylase in the liver. Purification of cholesterol 7 alpha-hydroxylase and the immunochemical evidence for the induction of cholesterol 7 alpha-hydroxylase by cholestyramine and circadian rhythm.

Title

Regulation of cholesterol 7 alpha-hydroxylase in the liver. Purification of cholesterol 7 alpha-hydroxylase and the immunochemical evidence for the induction of cholesterol 7 alpha-hydroxylase by cholestyramine and circadian rhythm.

Creator

Chiang J Y; Miller W F; Lin G M

Publisher

The Journal of biological chemistry

Date

1990
1990-03

Description

Two cholesterol 7 alpha-hydroxylase isozymes were purified from liver microsomes of cholestyramine-treated female rats by using anion exchange high performance liquid chromatography. These two cytochrome P-450 isozymes were similar in electrophoretic mobility, immunocross-reactivity, and Vmax but differed in Km for cholesterol, turnover number, and charges. Antibody against the major isozyme was raised in rabbit. This antibody specifically inhibited microsomal cholesterol 7 alpha-hydroxylase activity. Immunoblot of microsomal polypeptides indicated that microsomal cholesterol 7 alpha-hydroxylase enzyme levels were increased in parallel with cholesterol 7 alpha-hydroxylase activity upon the treatment of rats with diet supplemented with cholestyramine. Both cholesterol 7 alpha-hydroxylase activity and enzyme levels were drastically reduced immediately after the removal of cholestyramine from the diet. Cholesterol 7 alpha-hydroxylase activity was also detected in the microsomes of kidney, heart, and lung in about 7-27% of the level found in the liver. 3-Methylcholanthrene treatment induced cholesterol 7 alpha-hydroxylase activity and enzyme level. In contrast, pregnenolone-16 alpha-carbonitrile or dexamethasone treatment greatly depressed enzyme and activity in rats. Cholesterol 7 alpha-hydroxylase enzyme level was 2-3-fold higher in liver microsomes of rats maintained under the reversed light cycle than under the normal light cycle. In genetically obese Zucker rats, cholesterol 7 alpha-hydroxylase activity and enzyme level did not respond to the change in the light cycle, however, were induced to the same levels as in the lean rats by cholestyramine treatment. This study provided the first direct evidence that the bile acid feedback regulation and circadian rhythm of microsomal cholesterol 7 alpha-hydroxylase activity involved the induction of cholesterol 7 alpha-hydroxylase enzyme level.

Subject

Animals; Rats; Organ Specificity; Kinetics; *Circadian Rhythm; Enzyme Induction; Liver/drug effects/*enzymology; Cholesterol 7-alpha-Hydroxylase/*biosynthesis/isolation & purification/metabolism; Cholestyramine Resin/*pharmacology; Chromatography; Durapatite; Hydroxyapatites; Isoenzymes/*biosynthesis/isolation & purification; Obesity/enzymology; Polyethylene Glycols; Steroid Hydroxylases/*biosynthesis; Inbred Strains; Zucker; Microsomes; Ion Exchange

Rights

Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).

Pages

3889–3897

Issue

7

Volume

265

Citation

Chiang J Y; Miller W F; Lin G M, “Regulation of cholesterol 7 alpha-hydroxylase in the liver. Purification of cholesterol 7 alpha-hydroxylase and the immunochemical evidence for the induction of cholesterol 7 alpha-hydroxylase by cholestyramine and circadian rhythm.,” NEOMED Bibliography Database, accessed December 3, 2021, https://neomed.omeka.net/items/show/5348.

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