Terpenoid biosynthesis in Euphorbia lathyris and Copaifera spp

Abstract

Biosynthesis of triterpenoids (triterpene esters and triterpenols) by isolated latex ofEuphorbia lathyris was investigated. The rate of in vitro incorporation of mevalonic acid (0.55 nmol 100 p.1 latex 1 h-1 ) into triterpenoids was thirty times greater than acetate incorporation (0.02 nmol 100 41 latex 1 tn), 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 (15,000g 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 mevatonate to triterpenoids converting activity.Both HMG-CoA reductase (EC 1.1.1.34) and HMG-CoA lyase (EC 4.1.3.4) activities were detected in isolated latex. HMG-CoA reductase was localized to a membrane-bound fraction of a 5000g pellet of latex. The rate of conversion of HMG-CoA to mevalonate by this enzyme (0.02 nmol 100 p.1 latex -1 h.t) 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 (18,000g), and was solubilized by treatment with 2% polyoxyethylene ether W-1. Differences in the optimal pH for activity of HMG-CoA reductase from 1 the latex and vegetative 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 fromCopaifera 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 aUocatibn to the terpenes.Mevalonate incorporation by Copaifera Iangsdorfii 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. ACKNOWLEDGEM ENTSI thank Professor Melvin Calvin for providing me with the opportunity and the support to learn plant biochemistry in his labs. Members of the Calvin group not only helped me with my research but also ensured that it was not serious science at all times. I thank all those who spent time in the Calvin labs while I was there for their friendship, especially

Molecular cloning, expression and immunolocalization analysis of diphosphomevalonate decarboxylase involved in terpenoid biosynthesis from Euphorbia helioscopia L.

“…From our early observation of E. kansui Liou laticifers at early developmental stages, some endoplasmic reticulum dilated and coalesced to form small vacuoles, which began to accumulate latex particles, and then transport and release these latex particles into the central vacuole with their coalesce [37]. Skrukrud reported that mevalonic acid synthesize triterpenoid in the small vacuole of laticifers in Euphorbia Lathyri [38]. Fineran's ullrastructural observations indicated that latex particles were synthesized in tubular vacuoles in the peripheral cytoplasm of developing E. pulcherrima laticifers [39].…”