Biosynthesis of kaurene, squalene and phytoene from mevalonate-2-14C in a cell-free system from pea fruits

Kaurene, squalene and phytoene were identified as products from mevalonate-2- 14 C in a soluble system from young pea fruits. All three hydrocarbons were obtained when the incubation mixture contained ATP, Mg 2+ , Mn 2+ and pyridine nucleotides. Only squalene required pyridine nucleotides and only phytoene required Mn 2+ . The omission of pyridine nucleotides therefore leads to a specific exclusion of squalene synthesis and the omission of Mn 2+ to a specific exclusion of phytoene synthesis. In addition, the formation of squalene was inhibited over a certain range of Mn 2+ -concentrations, while the formation of phytoene was stimulated. Therefore the ratio of these two products was strongly dependent on the Mn 2+ -concentration. The formation of kaurene was optimal at a lower pH than that for the formation of the other products. Only kaurene synthesis was inhibited by the plant growth inhibitor AMO 1618. A mixed plastid and mitochondrial fraction greatly increased the formation of squalene, farnesol and geranylgeraniol but not the formation of phytoene and kaurene. One or more unidentified acids were also formed in the system.