-!- The alpha-subunit catalyzes the conversion of 1-C-(indol-3- yl)glycerol 3-phosphate to indole and D-glyceraldehyde 3-phosphate (this reaction was listed formerly as EC 4.1.2.8). -!- The indole migrates to the beta-subunit where, in the presence of pyridoxal 5'-phosphate, it is combined with L-serine to form L-tryptophan. -!- In some organisms this enzyme is part of a multifunctional protein that also includes one or more of the enzymes EC 2.4.2.18, EC 4.1.1.48, EC 4.1.3.27 and EC 5.3.1.24. -!- In thermophilic organisms, where the high temperature enhances diffusion and causes the loss of indole, a protein similar to the beta subunit can be found (EC 4.2.1.122). -!- That enzyme cannot combine with the alpha unit of EC 4.2.1.20 to form a complex.