Abstract
A latex pellet fraction from Euphorbia lathyris incorporates mevalonate into triterpenols and their fatty acid esters. Conditions for improved incorporation were determined. CaCl(2) or CaCl(2) plus MnCl(2) stimulated biosynthesis, and the metal ion chelator, ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA) enhanced stimulation. Ethylenediaminetetraacetic acid was almost as effective as EGTA, but phthalic acid and citric acid were relatively poor stimulators. The concentration of the Ca(2+)-EGTA complex was directly measured, and the incorporation data are best fitted by a curve that shows that the receptor for the complex is saturable. In the presence of the metal-chelate complex, the addition of fructose, 1,6-bisphosphate plus aldolase (triose-P) or malate provided additional stimulation. Incorporation was maximum at 40 micromolar R-mevalonate, and inhibition occurred at higher concentrations. The apparent K(m) for R-mevalonate was 15 micromolar. Under improved reaction conditions, the rate of triterpenoid biosynthesis from mevalonate is 25 times faster than was previously observed (GJ Piazza, EJ Saggese, KM Spletzer [1987] Plant Physiol 83: 177-180).