Phosphoribosylanthranilate isomerase

This enzyme [EC 4.1.3.27] catalyzes the reaction of chorismate with glutamine to generate anthranilate, pyruvate, and glutamate. In certain species, this enzyme is part of a multifunctional protein together with one or more other components of the system for the biosynthesis of tryptophan (Le., indole-3-glycerol-phosphate synthase, anthranilate phosphoribosyltransferase, tryptophan synthase, and phosphoribosylanthranilate isomerase). The anthranilate synthase that is present in these complexes has been reported to be able to utilize either glutamine or ammonia as the nitrogen source. However, it has also been reported that when anthranilate synthase is separated from this complex, only ammonia can serve as a substrate. 

In the biosynthesis pathways of histidine and tryptophan, the enzymes HisA (N -[(5 -phosphoribosyl)formimino]-5-aminoimidazole-4-carboxamide ribonucleotide isomerase) and TrpF (PRAI,phosphoribosylanthranilate isomerase) (Figure 16.13), both of which are ()3a)8-barrels, both catalyze Amadori rearrangements of a ther-molabile aminoaldose into the corresponding aminoketose (Figure 16.13). 

Figure 6 Amadori rearrangements catalyzed by HisA [A/-(5 -phospho-L-ribosyl-formimino)-5-amino-1 -(5 -phosphoribosyl)-4-imidazolecarboxamide isomerase] and TrpF (phosphoribosylanthranilate isomerase).

R. Sterner, A. Meiz, R. Thoma, and K. Kirsehner, Phosphoribosylanthranilate isomerase and indoleglyeerol-phosphate syndiase Tryptophan biosynthetie enzymes from Thermotoga maritima, Meth. Enzymol, 331 (2001) 270—280. 

Phosphoribosylanthranilate isomerase (PRAI) (EC 2.4.2.18) catalyzes the penultimate step in tryptophan biosynthesis. In contrast to the enzyme firom meso-philes, TmPRAI is again a homodimer showing thermal stability up to 95°. Under... 

Abbreviations ADCA, adipyl-cephalosporic acid epPCR, error-prone PCR IGPS, indole-3-glycerol phosphate synthase MO, monooxygenase MS, mutator strain PRAI, phosphoribosylanthranilate iso-merase ProFARI, N -[5-phosphoribosyl)formimino]-5-aminoimidazole-4-carboxylamide ribonucleotide isomerase SDM, site-directed mutagenesis, StEP, staggered extension process... 

In Figure 5.41 are depicted the early steps of the lAA biosynthesis in Ara-bidopsis leading to Trp (Figure 5.41). Chorismate (CHO) is converted into anthranilate (ANA) through the catalysis of the a and p subunits of ANA synthetase. Phosphoribosylanthranilate transferase (PAT) and phosphoribo-sylanthranilate isomerase (PAI) control the two successive steps, producing... 

Figure 5.41 Early steps of the proposed indole acetic acid biosynthesis pathways for Ara-bidopsis. CHO, chorismate ANA, anthranilate PANA, 5-phosphoribosylanthranilate CADP, l-(o-carboxyphenylamino)-l-deoxyribulose-5-phosphate IGP, indole-3-glycerol phosphate TRP, tryptophan. Enzymes ASA, anthranilate synthetase, suhunit a ASB, anthranilate synthetase, suhunit P PAT, phosphorihosylanthranUate transferase PAI, phosphoiibosylanthrani-late isomerase IGS, indole-3-glycerol-phosphate synthase TSA, tryptophan synthase, subunit a and TSB, tryptophan synthase, suhunit p.

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