The Effect of Cholesterol Feeding and Fasting upon P-Hydroxy- ,&methylglutaryl Coenzyme A Reductase*

The enzymatic reduction of /Shydroxy-P-methylglutaryl coenzyme A to mevalonic acid has been measured in cellfree systems prepared from the livers of rats maintained under various dietary conditions. It has been shown that the reductase reaction is markedly depressed when cholesterol is fed. This diminished activity has been observed in both the microsomes and in the subsequently solubilized preparation when an acetone powder technique is used. The effect of fasting upon fl-hydroxy-/3-methylglutaryl coenzyme A reduction has been examined and the results also show a dramatic decrease in the reductase activity in both the microsomes and the solubilized enzyme.