Phosphoribosylanthranilate

This enzyme [EC 2.4.2.18], also referred to as phospho-ribosyl-anthranilate pyrophosphorylase, catalyzes the reaction of anthranilate with phosphoribosylpyrophos-phate to produce A-5 -phosphoribosylanthranilate and pyrophosphate. 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 (i.e., indole-3-glycerol-phosphate synthase, anthranilate synthase, tryptophan synthase, and phos-phoribosylanthranilate isomerase). 

Among different organisms the five enzyme activities required for tryptophan synthesis are distributed on different proteins (table 21.1). For example, in E. coli, indoleglycerol phosphate synthase catalyzes both the isomerization of phosphoribosylanthranilate and the cyclization step. Of particular interest is the occurrence of a single protein of the catalytic activities for nonconsecutive reactions in some cases. If in such cases the proteins were separate from each other in the cell, this arrangement, for example, in Neurospora, would necessitate the product of one reaction leaving the product site of one enzyme to be acted on by another... 

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). 

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... 

PRPP is the activated intermediate in the synthesis of phosphoribosylamine in the de novo pathway of purine formation of purine nucleotides from free bases by the salvage pathway of orotidylate in the formation of pyrimidines of nicotinate ribonucleotide of phosphoribosyl ATP in the pathway leading to histidine and of phosphoribosylanthranilate in the pathway leading to tryptophan. 

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).

The pearl necklace model for the BSA-dodecylsulphate complexes is very different from the model used to interpret the neutron diffraction data for the complexes formed between the deuterated bifunctional enzyme N-5 -phosphoribosylanthranilate/indole-3-glycerol-phosphate... 

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... 

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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