Involved in monoterpene indole alkaloids (MIAs) biosynthesis. Converts by cyclization the strictosidine-derived geissoschizine to the sarpagan alkaloid polyneuridine aldehyde. Converts by aromatization the tetrahydro-beta-carboline alkaloids tetrahydroalstonine and ajmalicine to the corresponding beta-carboline alkaloids alstonine and serpentine, respectively