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 18.104.22.168
). 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 22.214.171.124
(anthranilate phosphoribosyltransferase), EC 126.96.36.199
(indole-3-glycerol-phosphate synthase), EC 188.8.131.52
(anthranilate synthase) and EC 184.108.40.206
(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 220.127.116.11
). That enzyme cannot combine with the alpha unit of EC 18.104.22.168
to form a complex.