<p>Tryptophan synthase catalyzes the last step in the biosynthesisof tryptophan [<cite idref="PUB00000116"/>, <cite idref="PUB00000769"/>]:<reaction>L-serine + 1-(indol-3-yl)glycerol 3-phosphate = L-tryptophan + glyceraldehyde 3-phosphate + H₂O</reaction>It has two functional domains, each found in bacteria and plants on aseparate subunit: alpha chain (<db_xref db="INTERPRO" dbkey="IPR002028"/>) is for the aldol cleavage of indoleglycerol phosphate to indole andglyceraldehyde 3-phosphate and beta chain is for the synthesis of tryptophan fromindole and serine. In fungi the two domains are fused together on a single multifunctional protein [<cite idref="PUB00004683"/>].</p><p>The beta chain of the enzyme, represented here, requires pyridoxal-phosphate as a cofactor. The pyridoxal-phosphate group is attached to a lysine residue. The region around this lysine residue also contains two histidine residues which are part of the pyridoxal-phosphate binding site.</p> Tryptophan synthase, beta chain