Enzymes involved in the metabolism of 3-hydroxy-3-methylglutaryl-coenzyme A in Catharanthus roseus

Abstract

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) is an important intermediate in various metabolic pathways, e.g. sterol biosynthesis, ketogenesis and leucine catabolism. The reactions and enzymes involved in the metabolism of HMG-CoA are briefly reviewed. These enzymes have been studied in Catharanthus roseus, a model system for studies on the regulation of secondary metabolic pathways, particularly those leading to terpenoidindole alkaloids. By using HPLC, three HMG-CoA catabolizing enzyme activities have been detected in protein extracts from suspension cultured C. roseus cells: HMG-CoA lyase, 3′-nucleotidase and (tentatively identified) 3-methylglutaconyl-CoA hydratase (HMG-CoA hydrolyase). The enzymes have been partially purified. HMG-CoA is formed from three molecules of acetyl-CoA, via reactions which are catalyzed by two (as in yeast and animal cells, via intermediacy of acetoacetyl-CoA) or by just one enzyme (as in e.g. radish). It is yet not clear which process occurs in C. roseus.