This cytosolic sesquiterpenoid synthase requires a divalent cation cofactor (Mg2+ or, to a lesser extent, Mn2+) to neutralize the negative charge of the diphosphate leaving group. While unlikely to encounter geranyl diphosphate (GDP) in vivo as it is localized to plastids, the enzyme can use GDP as a substrate in vitro to produce (+)-(4R)-limonene [cf. EC 4.2.3.20, (R)-limonene synthase]. The enzyme is induced as part of a defense mechanism in the grand fir Abies grandis as a response to stem wounding.
Terpenoid-based defenses in conifers: cDNA cloning, characterization, and functional expression of wound-inducible (E)-alpha-bisabolene synthase from grand fir (Abies grandis).
