Initial cyclization probably gives biyclogermacrene in an enzyme bound form which is not released to the medium. The enzyme from Solidago canadensis also forms a small amount of (+)-gamma-gurjunene .
initial step is the formation of a germacrenyl cation after abstraction of the diphosphate group. Internal shifts of electron pairs lead to the patchoulenyl cation, which then undergoes a double 1,2-hydride shift. Rearrangement leads to the aromadendrenyl cation, which then undergoes a 1,2-hydride shift. Abstraction of a proton by the enzyme yields isoledene, which is reprotonated at the active site of the enzyme. At this junction two proton abstractions are possible, one leading to (-)-alpha-gurjunene and the other to (+)-gamma-gurjunene