Liver 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity in pyridoxine-deficient rats.

The activities of 3-hydroxy-3-methylglutaryl-CoA reductase [EC 1.1.1.34] in the livers of pyridoxine-deficient and control rats were compared. The reductase activity, which is known to show a circadian rhythm, was about twice as high in pyridoxine-deficient rats during both the light and dark periods. After administration of cycloheximide the rate of decrease in reductase activity was similar in pyridoxine-deficient and control rats. The Km values from the two groups for DL-DMH-CoA, the heat stabilitied and the microsomal lipid compositions were also similar. The effects of cytosolic activator and inactivator proteins on the reductase activities were also similar. These results show that the increased activity in pyridoxine-deficient rats is due to increased enzyme synthesis or increased specific activity induced by some unknown mechanism, but not to change in the state of phosphorylation of the enzyme.