A pyridoxal-phosphate protein. The alpha-subunit catalyses the conversion of 1-C-(indol-3-yl)glycerol 3-phosphate to indole and D-glyceraldehyde 3-phosphate (this reaction was included formerly under 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 (anthranilate phosphoribosyltransferase), EC
4.1.1.48 (indole-3-glycerol-phosphate synthase), EC
4.1.3.27 (anthranilate synthase) and EC
5.3.1.24 (phosphoribosylanthranilate isomerase). 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.
