HMGCOA REDUCTASE AND CHOLESTEROL 7-ALPHA-HYDROXYLASE IN HUMAN-LIVER

The activities of HMGCoA [3-hydroxy-3-methylglutarylCoA] reductase and cholesterol 7.alpha.-hydroxylase were assayed in liver biopsies of patients with or without cholestyramine treatment. The active dephosphorylated form of HMGCoA reductase and the activity of cholesterol 7.alpha.-hydroxylase were under the detection limits in untreated subjects. After cholestyramine treatment activities of both enzymes were stimulated and the active form of HMGCoA reductase became detectable in 4 out of the 5 tested patients. In 2 subjects who received cholestyramine, the effect of exogenously added [4-14C]cholesterol on cholesterol 7.alpha.-hydroxylase was tested. In the presence of Tween 80, the detergent by which [14C]cholesterol was suspended, the enzyme activity was profoundly inhibited and synthesis of 7.alpha.-hydroxycholesterol was extremely low.