Biosynthesis of 3S-hydroxy-3-methylglutaryl-coenzyme A in Catharanthus roseus: acetoacetyl-CoA thiolase and HMG-CoA synthase show similar chromatographic behaviour

In eukaryotic terpenoid/sterol biosynthesis, 3S-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) is an important intermediate. In yeast and animal cells, two enzymes, acetoacetyl-CoA thiolase (AACT, EC 2.3.1.9) and HMG-CoA synthase (HMGS, EC 4.1.3.5) are required for the biosynthesis of HMG-CoA. These activities have now been partially purified from Catharanthus roseus (L.) G. Don plants. Although several purification steps 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 preparation 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)