Terpenoid biosynthesis in Euphorbia lathyris and Copaifera spp

Biosynthesis of triterpenoids (triterpene esters and triterpenols) by isolated latex of Euphorbia lathyris was investigated. The rate of in vitro incorporation of mevalonic acid (0.55 nmol 100 {dollar}mu{dollar}l latex{dollar}sp{lcub}-1{rcub}{dollar}h{dollar}sp{lcub}-1{rcub}{dollar}) into triterpenoids was thirty times greater than acetate incorporation (0.02 nmol 100 {dollar}mu{dollar}l latex{dollar}sp{lcub}-1{rcub}{dollar}h{dollar}sp{lcub}-1{rcub}{dollar}), indicating that the rate-limiting step in the pathway occurs prior to mevalonate. A particulate fraction, capable of converting mevalonate but not acetate into triterpenoids (15,000{dollar}g{dollar} pellet), showed a linear rate of triterpenoid biosynthesis over a period of four hours. No evidence was found to indicate that soluble latex proteins had an effect on either the biosynthesis or the removal of triterpenoids from this fraction. Electron micrographs of isolated E. lathyris latex showed the presence of latex particles and rod-shaped starch grains as well as a single-membrane-bounded structure which comigrated on Percoll gradients with the mevalonate to triterpenoids converting activity.; Both HMG-CoA reductase (EVC 1.1.1.34) and HMG-CoA lyase (EC 4.1.3.4) activites were detected in isolated latex. HMG-CoA reductase was localized to a membrane-bound fraction of a 5000{dollar}g{dollar} pellet of latex. The rate of conversion of HMG-CoA to mevalonate by this enzyme (0.02 nmol 100 {dollar}mu{dollar}l latex{dollar}sp{lcub}-1{rcub}{dollar}h{dollar}sp{lcub}-1{rcub}{dollar}) is comparable to the overall rate of acetate incorporation into the triterpenoids suggesting that this enzyme is rate-determining in the biosynthesis of triterpenoids in E. lathyris latex.; HMG-CoA reductase of E. lathyris vegetative tissue was localized to the membrane-bound portion of a particulate fraction (18,000{dollar}g{dollar}), and was solubilized by treatment with 2% polyoxyethylene ether W-1. Differences in the optimal pH for activity of HMG-CoA reductase from the latex and vegatative tissue suggest that isozymes of the enzyme may be present in the two tissue types.; Studies of the incorporation of various precursors into leaf discs and cuttings taken from Copaifera spp. show differences in the rate of incorporation into Copaifera sesquiterpenes suggesting that the site of sesquiterpene biosynthesis may differ in its accessability to the different substrates and/or reflecting the metabolic controls on carbon allocation to the terpenes. Mevalonate incorporation by Copaifera langsdorfii cuttings into sesquiterpenes was a hundred-fold greater than either acetate or glucose incorporation, however, its incorporation into squalene and triterpenoids was also a hundred-fold greater than the incorporation into sesquiterpenes.