Terpenoid biosynthesis in Euphorbia lathyris and Copaifera spp
Biosynthesis of triterpenoids by isolated latex of Euphorbia lathyris was investigated. The rate of in vitro incorporation of mevalonic acid into triterpenoids was thirty times greater than acetate incorporation indicating that the rate-limiting step in the pathway occurs prior to mevalonate. 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 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 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 from Copaifera spp. show differences in the rate of incorporation into Copaifera sesquiterpenes suggesting that the site of sesquiterpene biosynthesis may differ in its accessibility 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. 119 refs., 58 figs., 16 tabs.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6124450
- Report Number(s):
- LBL-23915; ON: DE88001463
- Resource Relation:
- Other Information: Thesis; (Ph.D). Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Triterpenoid biosynthesis in Euphorbia lathyris
Related Subjects
59 BASIC BIOLOGICAL SCIENCES
COPAIFERA
BIOLOGICAL PATHWAYS
EUPHORBIA
TERPENES
BIOSYNTHESIS
CARBON 14 COMPOUNDS
ELECTRON MICROSCOPY
ENZYME ACTIVITY
LATEX
OXIDOREDUCTASES
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ELASTOMERS
ENZYMES
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
MICROSCOPY
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PLANTS
POLYMERS
RUBBERS
SYNTHESIS
TREES
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550501 - Metabolism- Tracer Techniques