Activation of rat liver microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase by NADPH. Effects of dietary treatments.

The sigmoidal curves observed for rat liver microsomal 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase with NADPH as the varied substrate were markedly affected by feeding the animals diets containing colestipol, mevinolin and colestipol or cholesterol. Feeding of mevinolin and colestipol decreased the S0.5 for NADPH from 270 to 40 microM, while cholesterol feeding increased the value to 1.3 mM. Immuno-blotting analysis revealed that the Mr 100,000 form of HMG-CoA reductase predominated in cases where the S0.5 value was lowest, and the Mr 200,000 species was the major form where the S0.5 values were highest. Activation of HMG-CoA reductase by NADPH was not due to conversion of the Mr 200,000 form to the 100,000 form.