ENZYMES INVOLVED IN THE METABOLISM OF 3-HYDROXY-3-METHYLGLUTARYL-COENZYME-A IN CATHARANTHUS-ROSEUS

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) is an important interm ediate in various metabolic pathways, e.g. sterol biosynthesis, ketoge nesis and leucine catabolism. The reactions and enzymes involved in th e metabolism of HMG-CoA are briefly reviewed. These enzymes have been studied in Catharanthus roseus, a model system for studies on the regu lation of secondary metabolic pathways, particularly those leading to terpenoid-indole alkaloids. By using HPLC, three HMG-CoA catabolizing enzyme activities have been detected in protein extracts from suspensi on cultured C. roseus cells: HMG-CoA lyase, 3'-nucleotidase and (tenta tively identified) 3-methylglutaconyl-CoA hydratase (HMG-CoA hydrolyas e). The enzymes have been partially purified. HMG-CoA is formed from t hree molecules of acetyl-CoA, via reactions which are catalyzed by two (as in yeast and animal cells, via intermediacy of acetoacetyl-CoA) o r by just one enzyme (as in e.g. radish). It is yet not clear which pr ocess occurs in C. roseus.