Five steps from chorismate, PRPP and serine. Humans cannot do this; tryptophan is an essential amino acid
Route: Chorismate → Anthranilate + 5-Phosphoribosyl 1-pyrophosphate → N-(5-Phosphoribosyl)anthranilate → 1-(2-Carboxyphenylamino)-1-deoxyribulose 5-phosphate → Indole-3-glycerol phosphate + Serine → Tryptophan + Glyceraldehyde 3-phosphate
Anthranilate synthase has two parts. One releases ammonia from glutamine, and the other uses that ammonia to replace the hydroxyl group of chorismate and then splits off pyruvate, which leaves anthranilate. Anthranilate takes the ribose phosphate of PRPP and PPᵢ leaves. The ribose ring opens and rearranges to a keto sugar in the next step, and the step after that closes the five-membered ring of indole with loss of CO₂ and water. In E. coli the last two of these steps are done by one protein with two active sites. The final enzyme has two kinds of chains, alpha and beta. The alpha chain cuts indole-3-glycerol phosphate into indole and glyceraldehyde 3-phosphate. Indole travels through a tunnel inside the protein to the beta chain, where pyridoxal phosphate joins it to serine. The tunnel prevents loss of the indole to solution.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Anthranilate synthase | 4.1.3.27 | Glutamine | Glutamate, Pyruvate |
| 2 | Anthranilate phosphoribosyltransferase | 2.4.2.18 | PPᵢ | |
| 3 | Phosphoribosylanthranilate isomerase | 5.3.1.24 | ||
| 4 | Indole-3-glycerol phosphate synthase | 4.1.1.48 | CO₂, H₂O | |
| 5 | Tryptophan synthase | 4.2.1.20 |
Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).