  4.2.3.132 | (+)-copalyl diphosphate |
the enzyme converts geranylgeranyl diphosphate and the intermediate (+)-copalyl diphosphate to a nearly equal mixture of abietadiene (31%), levopimaradiene (34%), and neoabietadiene (28%), as well as to three minor products pimara-8(14),15-diene (3%), palustradiene (2%), and sandaracopimaradiene (2%) |
Abies grandis |
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| 4.2.3.132 | more |
abietadiene synthase catalyzes the cyclization and rearrangement of (E,E,E)-geranylgeranyl diphosphate to a mixture of abietadiene double-bond isomers. The enzyme is bifunctional: Protonation across the terminal 14-15 double bond of (E,E,E)-geranylgeranyl diphosphate followed by bicyclization and deprotonation, produces the stable intermediate (+)-copalyl diphosphate (CPP). Then the enzyme ionizes CPP to promote cyclization to the tricyclic perhydrophenanthrene backbone. However, this cyclization is further coupled to a 1,2-methyl migration, by means of intramolecular proton transfer within a pimarenyl intermediate, to generate the C13 isopropyl group characteristic of the abietane skeleton. Finally, deprotonation of the resulting abietenyl carbocation at one of three alternative positions (C7, C12, or C15) leads to the three principal olefin products abieta-7(8),13(14)-diene (abietadiene), abieta-8(14),12(13)-diene (levopimaradiene), and abieta-8(14)-13(15)-diene (neoabietadiene), respectively, as a function of pH |
Abies grandis |
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