Geranylgeranyl-diphosphate:isopentenyl-diphosphate transtransferase may refer to: Geranylfarnesyl diphosphate synthase, enzyme Hexaprenyl diphosphate synthase (geranylgeranyl-diphosphate specific), enzyme All-trans-nonaprenyl diphosphate synthase (geranylgeranyl-diphosphate specific), enzyme