Editing Tryptophan synthase (section)

==Enzyme structure==
[[Image:Active_Site_2.png|thumb|alt=caption.|Active sites for α and β subunits showing hypothesized catalytic residues|left]]

=== 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" />

=== Hydrophobic channel ===
The α and β active sites are separated by a 25 Ångstrom long [[hydrophobic]] channel contained within the enzyme allowing for the diffusion of indole. If the channel did not exist, the indole formed at an α active site would quickly diffuse away and be lost to the cell as it is hydrophobic and can easily cross membranes. As such, the channel is essential for enzyme complex function.<ref name="Channel">{{cite journal |vauthors=Huang X, Holden HM, Raushel FM | title = Channeling of Substrates and Intermediates in Enzyme-Catalyzes Reactions | journal =Annu Rev Biochem | volume = 70 | pages = 149–80 | year = 2001 | pmid = 11395405 | doi = 10.1146/annurev.biochem.70.1.149}}</ref>