Requires Mg2+. The enzyme gives 28% cubebol, 29% (-)-germacrene D, 10% (+)-delta-cadinene and traces of several other sesquiterpenoids. See also EC 18.104.22.168 (–)-germacrene D synthase and EC 22.214.171.124 (+)-delta-cadinene synthase.
Cop4 rearranges a secondary cisoid, allylic cation derived from farnesyl diphophate after isomerization (cis-trans pathway of catalysis) into multiple products, with delta-cadinene and beta-copaene as the major products when expressed in Escherichia coli
Cop4 is a catalytically promiscuous enzyme that cyclizes (E,E)-farnesyl diphophate into multiple products, including (-)-germacrene D and cubebol (major products). Conversion of (E,E)-farnesyl diphophate by Cop4 proceeds via an (E,E)-germacradienyl carbocation. Cop4 cyclizes (2Z,6E)-farnesyl diphophate via a (6S)-beta-bisabolyl cation intermediate to (6S)-beta-bisabolene. Cop4 converts E-geranyl diphophate into cyclic and acyclic monoterpenes. Cop4 also cyclizes nerolidyl diphosphate. Under alkaline (pH 10) or acidic (pH 5.0) conditions, Cop4 becomes a very selective germacrene D synthase
under both alkaline and acidic conditions Cop4 becomes a very selective enzyme with only one major product (-)-germacrene D compared to three major compounds produced under neutral reaction conditions. At pH 10, the cyclization reaction ends with the hydride shift and deprotonation of the germacradienyl cation to yield (-)-germacrene D, 91% of total sesquiterpene products, while at pH 5.0 cyclization can proceed via a 1,6 ring closure to also yield a small amount of delta-cadinene, 12% of total sesquiterpene products, in addition to (?)-germacrene D
increasing the reaction temperature to 37°C decreases the fidelity of Cop4. At 37°C Cop4 generates a relative larger fraction of products beta-cubebene, sativene, delta-cadinene and beta-copaene that are derived from a cadinyl cation intermediate