Editing Tryptophan synthase (section)

=== Subunits ===
Tryptophan synthase typically exists as an α-ββ-α complex. The α and β subunits have molecular masses of 27 and 43 kDa respectively. The α subunit has a [[TIM barrel]] conformation. The β subunit has a fold type II conformation and a binding site adjacent to the active site for monovalent cations.<ref name="Structure">{{cite journal |vauthors=Grishin NV, Phillips MA, Goldsmith EJ | title = Modeling of the spatial structure of ornithine decarboxylases | journal = Protein Sci | volume = 4 | issue = 7 | pages = 1291–304 |date=July 1995 | pmid = 7670372 | doi = 10.1002/pro.5560040705| pmc = 2143167 }}</ref> Their assembly into a complex leads to structural changes in both subunits resulting in reciprocal activation. There are two main mechanisms for intersubunit communication. First, the COMM domain of the β-subunit and the α-loop2 of the α-subunit interact. Additionally, there are interactions between the αGly181 and βSer178 residues.<ref name="Interaction">{{cite journal |vauthors=Schneider TR, Gerhardt E, Lee M, Liang PH, Anderson KS, Schlichting I | title = Loop closure and intersubunit communication in tryptophan synthase | journal = Biochemistry | volume = 37 | issue = 16 | pages = 5394–406 |date=April 1998 | pmid = 9548921 | doi = 10.1021/bi9728957}}</ref> The active sites are regulated allosterically and undergo transitions between open, inactive, and closed, active, states.<ref name="Regulation" />