Heterodimeric geranyl(geranyl)-diphosphate (GPP) synthase large subunit. In vitro, the large subunit catalyzes mainly the trans-addition of the three molecules of IPP onto DMAPP to form geranylgeranyl pyrophosphate while the small subunit alone is inactive. Upon association of the two subunits, the product profile changes and the production of gerany-diphosphate is strongly increased. dimethylallyl diphosphate + isopentenyl diphosphate = (2E)-geranyl diphosphate + diphosphate (2E)-geranyl diphosphate + isopentenyl diphosphate = (2E,6E)-farnesyl diphosphate + diphosphate (2E,6E)-farnesyl diphosphate + isopentenyl diphosphate = (2E,6E,10E)-geranylgeranyl diphosphate + diphosphate Binds 2 Mg(2+) ions per subunit. Isoprenoid biosynthesis; farnesyl diphosphate biosynthesis; farnesyl diphosphate from geranyl diphosphate and isopentenyl diphosphate: step 1/1. Isoprenoid biosynthesis; geranyl diphosphate biosynthesis; geranyl diphosphate from dimethylallyl diphosphate and isopentenyl diphosphate: step 1/1. Isoprenoid biosynthesis; geranylgeranyl diphosphate biosynthesis; geranylgeranyl diphosphate from farnesyl diphosphate and isopentenyl diphosphate: step 1/1. Monomer. Part of a heterodimeric geranyl(geranyl)diphosphate synthase. Interacts with GGR. Expressed ubiquitously. Belongs to the FPP/GGPP synthase family.