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Metabolism and Enzymology

Triterpene Biosynthesis in the Latex of Euphorbia lathyris

Calmodulin Antagonists Are Ineffective in Whole Latex

United State Department of Agriculture, Eastern Regional Research Center, Philadelphia, Pennsylvania 19118

The calmodulin antagonists chlorpromazine, fluphenazine, trifluoperazine, and 2-(pentachlorophenoxy)ethyl N,N-diethylamine are not inhibitors of acetate incorporation into triterpenols (TOH) and their fatty acid esters (TE) in whole tapped latex from Euphorbia lathyris, although prior work demonstrated that these antagonists are good inhibitors of mevalonate incorporation into TOH and TE in a centrifuged pellet from the latex. Antagonist absorption into the endogenous terpene pool is the primary reason for antagonist ineffectiveness in whole latex; changes in the utilized substrate or chemical deactivation of the antagonists were ruled out as factors. A biosynthetically inactive, latex supernatant fraction containing the endogenous terpene pool was prepared. This fraction blocks antagonist action when added to the latex pellet, and proved to be a useful tool for demonstrating that inhibition of triterpene biosynthesis by a calmodulin antagonist is partially reversible.