HMG-CoA reductase is the most important regulatory enzyme for the cholesterol biosynthetic pathway and other isoprenoids/terpenoids. HMG-CoA reductase catalyzes the reaction that follows:
HMG-CoA + 2 NADPH + H+ <=> Mevalonate + CoASH + 2 NADP+
HMG-CoA reductase is a target for drugs that attempt to lower cholesterol levels in the body. One such drug is lovastatin, which inhibits the enzyme and stops endogenous synthesis of cholesterol