What is "tryptophan synthase"

n. (context enzyme English) An enzyme found in plants and bacteria, but not in animals, which catalyses the final step in the biosynthesis of tryptophan.

Tryptophan synthase or tryptophan synthetase is an enzyme that catalyzes the final two steps in the biosynthesis of tryptophan. It is commonly found in Eubacteria, Archaebacteria, Protista, Fungi, and Plantae. However, it is absent from Animalia. It is typically found as an α2β2 tetramer. The α subunits catalyze the reversible formation of indole and glyceraldehyde-3-phosphate (G3P) from indole-3-glycerol phosphate (IGP). The β subunits catalyze the irreversible condensation of indole and serine to form tryptophan in a pyridoxal phosphate (PLP) dependent reaction. Each α active site is connected to a β active site by a 25 angstrom long hydrophobic channel contained within the enzyme. This facilitates the diffusion of indole formed at α active sites directly to β active sites in a process known as substrate channeling. The active sites of tryptophan synthase are allosterically coupled.

Tryptophan synthase (indole-salvaging) (, tryptophan synthase beta2) is an enzyme with systematic name L-serine hydro-lyase (adding indole, L-tryptophan-forming). This enzyme catalyses the following chemical reaction

L- serine + indole $\rightleftharpoons$ L- tryptophan + HO

This enzyme salvages the lost indole to L-tryptophan.