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 184.108.40.206). 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 220.127.116.11 (anthranilate phosphoribosyltransferase), EC 18.104.22.168 (indole-3-glycerol-phosphate synthase), EC 22.214.171.124 (anthranilate synthase) and EC 126.96.36.199 (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 188.8.131.52). That enzyme cannot combine with the alpha unit of EC 184.108.40.206 to form a complex.
consists of an alpha2beta2 bienzyme complex with alphabeta dimeric units assembled as the tetrameric species via the beta-beta subunit interface, each alpha-subunit catalyzes the cleavage of 3-indole-D-glycerol 3'-phosphate to indole and D-glyceraldehyde 3-phosphate, the pyridoxal phosphate requiring beta-subunit catalyzes a beta-replacement reaction in which indole replaces the hydroxyl of L-Ser, giving L-Trp
subunit TrpA catalyzes the reversible cleavage of indole-3-glycerol phosphate (IGP1) into glyceraldehyde-3-phosphate and indole, the indole migrates through a hydrophobic channel to an active site of an attached TrpB1 subunit, where it condenses with L-serine in a pyridoxal phosphate dependent irreversible reaction to form L-tryptophan