Class I hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase (HMGR)
Hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase (HMGR), class I enzyme, homotetramer. Catalyzes the synthesis of coenzyme A and mevalonate in isoprenoid synthesis. In mammals this is the rate limiting committed step in cholesterol biosynthesis. Class I enzymes are found predominantly in eukaryotes and contain N-terminal membrane regions. With the exception of Archaeoglobus fulgidus, most archeae are assigned to class I, based on sequence similarity of the active site, even though they lack membrane regions. Yeast and human HMGR are divergent in their N-terminal regions, but are conserved in their active site. In contrast, human and bacterial HMGR differ in their active site architecture.