Regulation of the Biosynthesis of Ent-Kaurene from Mevalonate in the Endosperm of Immature Marah macrocarpus Seeds by Adenylate Energy Charge

The rate of kaurene biosynthesis from mevalonate in a cell-free enzyme preparation from the endosperm of immature seeds of Marah macrocarpus is regulated by adenylate energy charge. The response curve is typical of a biosynthetic energy-utilizing sequence in which the rate of biosynthesis increases sharply as the energy charge is increased above 0.80. ADP proved to be an effective inhibitor of this process. AMP gave no inhibition at concentrations up to 2 mm and orthophosphate gave no inhibition up to 15 mm. Measurement of the pool sizes of intermediates in the sequence showed that the presence of ADP caused an increase in the levels of 5-phosphomevalonate and 5-pyrophosphomevalonate and a decrease in the levels of isopentenyl pyrophosphate and kaurene. These results indicate that pyrophosphomevalonate decarboxylase is the enzyme most subject to regulation by adenylate energy charge. The rate of conversion of isopentenyl pyrophosphate to kaurene and the rate of utilization of mevalonate by mevalonate kinase were not influenced by variations in the adenylate energy charge.