Phosphoribosyl

Hypoxanthme-guanine-xanthiiie phosphoribosyl transferase Dock 88... 

AMP, ADP, and ATP = adenosine mono-, di-, and triphosphate IMP = inosine 5 -monophosphate AICAR = 5 -phosphoribosyl-5-amino-4-imida2olecarboxamide DAP = diaminopimelic acid PRPP = phosphoribosyl pyrophosphate a — KGA = a-ketoglutaric acid Orn = ornithine Cit = citnilline represents the one carbon unit lost to tetrahydrofolate as serine is converted to glycine. 

Gene symbols are according to those of E. coli. (173). Abbreviations Horn, Homoserine Ant, Anthranilic acid PR, Phosphoribosyl ppc, Phosphoenolpyruvate carboxylase PRDH, prephenate dehydrogenase. 

Phosphoribosyl pyrophosphate synthetase (from human erythrocytes, or pigeon or chicken liver) [9015-83-2] Mr 60,000, [EC 2.7.6.1]. Purified 5100-fold by elution from DEAE-cellulose, fractionation with ammonium sulfate, filtration on Sepharose 4B and ultrafiltration. [Fox and Kelley J Biol Chem 246 5739 197h, Flaks Methods Enzymol6 158 1963 Kornberg et al. J Biol Chem 15 389 7955.]... 

Figure 4.6 The bifunctional enzyme PRA-isomerase (PRAI) IGP-synthase (IGPS) catalyzes two sequential reactions in the biosynthesis of tryptophan. In the first reaction (top half), which is catalyzed by the C-terminal PRAI domain of the enzyme, the substrate N-(5 -phosphoribosyl) anthranilate (PRA) is converted to l-(o-carboxyphenylamino)-l-deoxyribulose 5-phosphate (CdRP) by a rearrangement reaction. The succeeding step (bottom half), a ring closure reaction from CdRP to indole-3-glycerol phosphate (IGP), is catalyzed by the N-terminal IGPS domain.

Figure 4.7 Two of the enzymatic activities involved in the biosynthesis of tryptophan in E. coli, phosphoribosyl anthranilate (PRA) isomerase and indoleglycerol phosphate (IGP) synthase, are performed by two separate domains in the polypeptide chain of a bifunctional enzyme. Both these domains are a/p-barrel structures, oriented such that their active sites are on opposite sides of the molecule. The two catalytic reactions are therefore independent of each other. The diagram shows the IGP-synthase domain (residues 48-254) with dark colors and the PRA-isomerase domain with light colors. The a helices are sequentially labeled a-h in both barrel domains. Residue 255 (arrow) is the first residue of the second domain. (Adapted from J.P. Priestle et al., Proc.

Priestle, J.P, et al. Three-dimensional structure of the bifunctional enzyme N-(5 -phosphoribosyl) anthranilate isomerase-indole-3-glycerol-phosphate synthase from Escheriehia eoli. Proc. Natl. Aead. 

Guanine Phosphoribosyl Transferase. Guanine phosphoribosyl transferase (GPRT) is one of the enzymes of the purine salvage pathway, which is needed by protozoa because they lack the ability to synthesize purine nucleotides. 

Figure20-2. The pentose phosphate pathway. ( ,— PRPP, 5-phosphoribosyl 1-pyrophosphate.)...

Conversion of purines, their ribonucleosides, and their deoxyribonucleosides to mononucleotides involves so-called salvage reactions that require far less energy than de novo synthesis. The more important mechanism involves phosphoribosylation by PRPP (structure II, Figure 34-2) of a free purine (Pu) to form a purine 5 -mononucleotide (Pu-RP). 

Two phosphoribosyl transferases then convert adenine to AMP and hypoxanthine and guanine to IMP or GMP (Figure 34-4). A second salvage mechanism involves phosphoryl transfer from ATP to a purine ri-bonucleoside (PuR) ... 

Figure 34-4. Phosphoribosylation of adenine, hy-poxanthine,and guanine to form AMP, iMP, and GMP, respectively.

Chang H-K, GJ Zylstra (1999) Role of quinolinate phosphoribosyl transferase in degradation of phthalate by Burkholderia cepacia DBOl. J Bacteriol 181 3069-3075. 

Wang K, K Conn, G Lazarovits (2006) Involvement of quinolinate phosphoribosyl transferase in promotion of potato growth by a Burkholderia strain. Appl Environ Microbiol 72 760-768. 

Seasonal variations in the metabolic fate of adenine nucleotides prelabelled with [8—1-4C] adenine were examined in leaf disks prepared at 1-month intervals, over the course of 1 year, from the shoots of tea plants (Camellia sinensis L. cv. Yabukita) which were growing under natural field conditions by Fujimori et al.33 Incorporation of radioactivity into nucleic acids and catabolites of purine nucleotides was found throughout the experimental period, but incorporation into theobromine and caffeine was found only in the young leaves harvested from April to June. Methy-lation of xanthosine, 7-methylxanthine, and theobromine was catalyzed by gel-filtered leaf extracts from young shoots (April to June), but the reactions could not be detected in extracts from leaves in which no synthesis of caffeine was observed in vivo. By contrast, the activity of 5-phosphoribosyl-1-pyrophosphate synthetase was still found in leaves harvested in July and August. 

J3. Jolly, D. J., Okayama, H Berg, P., Esty, A. C., Filpula, D Bohlen, P., Johnson, G. G., Shively, J. E., Hunkapillar, T., and Friedmann, T., Isolation and characterization of a full-length expressible cDNA for human hypoxanthine phosphoribosyl-transferase. Proc. Natl. Acad. Sci. U.S.A. 80,477-481 (1983). 

Marcus, S.L., and Balbinder, E. (1972) Use of affinity matrices in determining steric requirements for substrate binding Binding of anthranilate 5-phosphoribosyl-pyrophosphate phosphoribosyltransferase from Salmonella typhimurium to Sepharose-anthranilate derivatives. Anal. Biochem. 48, 448-459. 

The answer is c. (Katzung, p 933.) Resistance to thioguanine occurs because of an increase in alkaline phosphatase and a decrease in hypoxanthine-guanine phosphoribosyl transferase. These enzymes are responsible, respectively, for the increase in dephosphorylation of thiopurine nucleotide and the conversion of thioguanine to its active form, 6-thioinosinic acid. 

Wu, C. L. and Melton, D. W. Production of a model for Lesch-Nyhan syndrome in hypoxanthine phosphoribosyl-transferase-deficient mice. Nat. Genet. 3 235-240,1993. 

NAGY, P.L., MCCORKLE, G.M., ZALKIN, H., purU, A source of formate for purT-dependent phosphoribosyl-Y-formylglycinamide synthesis, J. Bacteriol., 1993, 175, 7066-7073. 

There was no increase in mutation frequency at the hypoxanthine-guanine phosphoribosyl transferase gene locus in the presence or absence of S9 (Bootman et al. 1988b), and results were negative in a DNA repair assay with E. coli (Hodson-Walker and May 1988). 

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