BIOSYNTHESIS OF 3S-HYDROXY-3-METHYLGLUTARYL-COENZYME-A IN CATHARANTHUS-ROSEUS - ACETOACETYL-COA THIOLASE AND HMG-COA SYNTHASE SHOW SIMILAR CHROMATOGRAPHIC BEHAVIOR

In eukaryotic terpenoid/sterol biosynthesis, 3S-hydroxy-3-methylglutar yl-coenzyme A (HMG-CoA) is an important intermediate. In yeast and ani mal cells, two enzymes, acetoacetyl-CoA thiolase (AACT, EC 2.3.1.9) an d HMG-CoA synthase (HMGS, EC 4.1.3.5) are required for the biosynthesi s of HMG-CoA. These activities have now been partially purified from C atharanthus roseus (L.) G. Don plants. Although several purification s teps were applied, HMGS activity was not separated from AACT activity. A direct high-performance liquid chromatographical assay established the presence of both activities unequivocally. The purified preparatio n was free of specific HMG-CoA metabolizing enzyme activities: HMG-CoA lyase (HMGL, EC 4.1.3.4), HMG-CoA reductase (HMGR, EC 1.1.1.34) and 3 -methylglutaconyl-CoA hydratase (MGH, EC 4.2.1.18). The formation of H MG-CoA from acetyl-CoA as single substrate suggests that both AACT and HMGS activities are involved in HMG-CoA biosynthesis, a situation sim ilar to that in yeast and animal cells.