Pathway · 2 proteins
Aromatic amino acids
Shikimate and chorismate chemistry supplies aromatic branches.
How it works
- Erythrose-4-phosphate and phosphoenolpyruvate feed the shikimate pathway.
- A series of enzyme-catalysed transformations produces chorismate, a branch point for several aromatic products.
- Phenylalanine, tyrosine and tryptophan follow distinct branches from that shared supply. Individual organism-specific alternatives and enzyme assignments must be checked against the cited annotations and pathway literature.
Grouped by the atlas’s curated pathway map. The table order is not a proven reaction order.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Anthranilate phosphoribosyltransferase | 2.4.2.18 | N-(5-phospho-beta-D-ribosyl)anthranilate + diphosphate = 5-phospho-alpha-D-ribose 1-diphosphate + anthranilate | 5-phospho-alpha-D-ribose 1-diphosphate, Mg(2+) | 340 | Step named |
| N-(5'-phosphoribosyl)anthranilate isomerase | 5.3.1.24 | N-(5-phospho-beta-D-ribosyl)anthranilate = 1-(2-carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate | — | 204 | Step named |
Also part of this pathway
These proteins are described under another pathway, but also take part here.
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Chorismate synthaseHome: Aromatic amino acids | 4.2.3.5 | 5-O-(1-carboxyvinyl)-3-phosphoshikimate = chorismate + phosphate | FMN | 398 | Step named |
| p-aminobenzoate synthetaseHome: Aromatic amino acids | — | — | — | 348 | Step named |
| 3-phosphoshikimate 1-carboxyvinyltransferaseHome: Aromatic amino acids | 2.5.1.19 | 3-phosphoshikimate + phosphoenolpyruvate = 5-O-(1-carboxyvinyl)-3-phosphoshikimate + phosphate | — | 431 | Step named |
| Tryptophan synthase alpha chainHome: Aromatic amino acids | 4.2.1.20 | (1S,2R)-1-C-(indol-3-yl)glycerol 3-phosphate + L-serine = D-glyceraldehyde 3-phosphate + L-tryptophan + H2O | — | 262 | Step named |
| prephenate dehydrogenaseHome: Aromatic amino acids | 1.3.1.12 | prephenate + NAD(+) = 3-(4-hydroxyphenyl)pyruvate + CO2 + NADH | — | 311 | Step named |
| Indole-3-glycerol phosphate synthaseHome: Aromatic amino acids | 4.1.1.48 | 1-(2-carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate + H(+) = (1S,2R)-1-C-(indol-3-yl)glycerol 3-phosphate + CO2 + H2O | — | 257 | Step named |
| Shikimate kinaseHome: Aromatic amino acids | 2.7.1.71 | shikimate + ATP = 3-phosphoshikimate + ADP + H(+) | Mg(2+) | 168 | Step named |
| Anthranilate synthase component IIHome: Aromatic amino acids | — | — | — | 197 | Step named |
| Anthranilate synthase component 1Home: Aromatic amino acids | 4.1.3.27 | chorismate + L-glutamine = anthranilate + pyruvate + L-glutamate + H(+) | Mg(2+) | 494 | Step named |
| Shikimate dehydrogenase (NADP(+))Home: Aromatic amino acids | 1.1.1.25 | shikimate + NADP(+) = 3-dehydroshikimate + NADPH + H(+) | — | 269 | Step named |
| Bifunctional chorismate mutase/prephenate dehydrataseHome: Aromatic amino acids | 4.2.1.51; 5.4.99.5 | chorismate = prephenate | — | 362 | Step named |
| Tryptophan synthase beta chain 1Home: Glycine, serine and threonine metabolism | 4.2.1.20 | (1S,2R)-1-C-(indol-3-yl)glycerol 3-phosphate + L-serine = D-glyceraldehyde 3-phosphate + L-tryptophan + H2O | — | 397 | Step named |
Origins
Could phenylalanine, tyrosine and tryptophan, with their ring structures, have formed before cells?
Miller and Orgel suggested some rather long synthetic routes to the aromatic amino acids. Cairns-Smith doubts that more than traces of them have ever been formed from very simple starting conditions, and notes that yields in simulation experiments are always low, sometimes very low.
Prebiotic syntheses give equal amounts of left- and right-handed amino acids; why proteins use only the left-handed forms is still an open question.
In the cell these amino acids are made by a branched pathway through shikimate and chorismate, using eleven proteins of the minimal set. Without them the cell would have to find these amino acids already made, and the books report no plausible prebiotic source.
From the books: Cairns-Smith, Genetic Takeover and the Mineral Origins of Life, p. 22; Garrett & Grisham, Biochemistry, PDF p. 131.
The wider question for this part of the cell: origins for making dna and rna letters.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: Purine biosynthesis · Pyrimidine biosynthesis · Interconversion and salvage · Deoxyribonucleotide supply · Purine metabolism · Pyrimidine metabolism · Histidine metabolism · Not yet placed in a pathway