Biosynthesis of monoterpene hydrocarbons from [1- 3H]neryl pyrophosphate and [1- 3H]geranyl pyrophosphate by soluble enzymes from Citrus limonum

A soluble enzyme preparation from the flavedo of Citrus limonum transforms [1- 3H 1]neryl pyrophosphate or [1- 3H 1]geranyl pyrophosphate into β-pinene, sabinene, α-pinene, and limonene. The enzyme has been partially purified and stabilized by precipitation with polyethyleneglycol. The enzymic cyclization requires the presence of Mn 2+, which cannot be replaced with Mg 2+. The addition of reagents containing sulfhydryl groups is essential for optimal activity. Allylic C 10 monophosphates do not act as substrates, but they inhibit hydrocarbon formation. Inorganic pyrophosphate has a similar inhibitory effect. No interconversion of neryl and geranyl pyrophosphate has been observed. Possible pathways for the enzymic cyclization reactions are proposed.