Prokaryotic tryptophan synthase, which catalyzes the last processes in the biosynthesis of tryptophan, is a multimeric αββα complex composed of nonidentical α and β subunits. The α and β subunits catalyze different reactions. The α-site cleaves (1S,2R)-1-C-(indol-3-yl)glycerol 3-phosphate (IGP) to give indole and d-glyceraldehyde 3-phosphate (G3P). The tryptophan-generating β-reaction requires a pyridoxal phosphate cofactor. In order to keep the two reactions in phase, the α-reaction and β-reaction regulate each other through allosteric interactions. Tryptophan synthase subunit alpha is also called as indole-3-glycerol-phosphate lyase.