α subunit reaction: The α subunit catalyzes the formation of indole and G3P from a retro-aldol cleavage of IGP.
The αGlu49 and αAsp60 are thought to be directly involved in the catalysis as shown.
The rate limiting step is the isomerization of IGP.
See image 2.

β subunit reaction: The β subunit catalyzes the β-replacement reaction in which indole and serine condense to form tryptophan in a PLP dependent reaction.
The βLys87, βGlu109, and βSer377 are thought to be directly involved in the catalysis as shown.
Again, the exact mechanism has not been conclusively determined.
See image 2.

Net reaction: See image 3.
α subunit reaction: The α subunit catalyzes the formation of indole and G3P from a retro-aldol cleavage of IGP. The αGlu49 and αAsp60 are thought to be directly involved in the catalysis as shown. The rate limiting step is the isomerization of IGP. See image 2.
β subunit reaction: The β subunit catalyzes the β-replacement reaction in which indole and serine condense to form tryptophan in a PLP dependent reaction. The βLys87, βGlu109, and βSer377 are thought to be directly involved in the catalysis as shown. Again, the exact mechanism has not been conclusively determined. See image 2.
Net reaction: See image 3.
Tryptophan synthase