In enzymology, a phosphoribosylanthranilate isomerase (PRAI) (EC 5.3.1.24) is an enzyme that catalyzes the third step of the synthesis of the amino acid tryptophan.

[2] This enzyme belongs to the family of isomerases, specifically those intramolecular oxidoreductases interconverting aldoses and ketoses.

Other names in common use include: Phosphoribosylanthranilate isomerase is one of the many enzymes within the biosynthesis pathway of tryptophan (an essential amino acid).

Within Saccharomyces cerevisiae, Bacillus subtilis, Pseudomonas putida, and Acinetobacter calcoaceticus the enzyme is monmeric.

The known 2.0 A structure of PRAI from Pyrococcus furiosus shows that tPRAI has a TIM-barrel fold (Fig.

Two long, symmetry-related loops that protrude reciprocally into cavities of the other subunit provide for multiple hydrophobic interactions.

Moreover, the side chains of the N-terminal methionines and the C-terminal leucines of both subunits are immobilized in a hydrophobic cluster, and the number of salt bridges is increased in tPRAI.

The following molecules have been shown to inhibit PRAI activity: Reduced 1-(2-carboxyphenylamino )-1-deoxy-D-ribulose 5-phosphate [5, 6,8); Indoleglycerol phosphate (8); Indolepropanol phosphate (8); MnCI2 CoCI2 [16); CuS04 (16); More (chemically synthesized N-(5-phospho-betaD-ribosyl)anthranilate contains inhibitors, but not if it is generated by anthranilate phosphoribosyltransferase) There are homologous genes which produce this enzyme in plant species such as Arabidopsis thaliana and Oryza sativa (Asian Rice).