Regulation of Cholesterol 7 α -Hydroxylase
Microsomal cholesterol 7 α-hydroxylase is the first and rate limiting enzyme in the conversion of cholesterol to bile acids in the liver. This enzyme activity is enhanced two to three fold by the treatment of rats with bile acid sequestrant, cholestyramine, and varies depending on animal species, sex and age. A cytochrome P-450 isozyme was isolated from cholestyramine-treated female rats and was active in reconstitution of cholesterol 7 α-hydroxylase activity with NADPH-cytochrome P-450 reductase and phospholipid. Phospholipid is required for optimal activity. Cytochrome b 5 could stimulate the reconstituted activity by two and half- fold. Reconstituted enzyme activity could be abolished by preincubation with alkaline phosphatase. On the other hand, cAMP-dependent protein kinase stimulated the activity by two and half-fold. These results suggest that reconstituted cholesterol 7 α-hydroxylase activity can be modulated by phosphorylation and dephosphorylation mechanism.
KeywordsBile Acid Liver Microsome Hydroxylase Activity Bile Acid Sequestrant Bacterial Alkaline Phosphatase
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