Guanine-xanthine phosphoribosyltransferase

Kelley, W.N., Greene, M.L., Rosenbloom, FM., Henderson, J.F., and Seegmiller, J.E. Hypo-xanthine-guanine phosphoribosyltransferase deficiency in gout. Ann. Intern. Med., 70 155,... 

PP-Ribose-P concentrations are much lower in Ehrlich ascites tumor cells in vivo than in vitro, and both PP-ribose-P levels and the rate of purine biosynthesis de novo are increased following the injection of glucose (SS). Both PP-ribose-P concentrations and rates of de novo s3mthesis are increased markedly in human skin fibroblasts which are deficient in hypo-xanthine-guanine phosphoribosyltransferase (3S), and this is probably related to the extraordinary rate of purine synthesis in vivo in patients with this enzyme deficiency (34). PP-Ribose-P levels are also elevated in some patients with gout and accelerated purine biosynthesis de novo (35,36). 

Fig. 3. Comparison of kinetic properties of normal and mutant hypo-xanthine-guanine phosphoribosyltransferase. Normal enzyme, solid line mutant enzyme, dotted line (From McDonald and Kelley, 1971).

Free guanine and hypo xanthine (the deamination product of adenine Fig. 22-45) are salvaged in the same way by hypoxanthine-guanine phosphoribosyltransferase. A similar salvage pathway exists for pyrimidine bases in microorganisms, and possibly in mammals. 

Besides this salvage role, hypoxanthine-guanine phosphoribosyltransferase is probably important also for the transfer of purines from liver to other tissues. Purine biosynthesis de novo is especially active in the liver, and extrahe-patic cells that have a low capacity for the synthesis of purines de novo, such as erythrocytes and bone marrow cells, depend on uptake of hypoxanthine and xanthine from the... 

Figure 10.6 HPLC elution profiles of an incubation mixture made up of. 2 nmol of hypoxanthine/guanine phosphoribosyltransferase, SO fiM guanine (G), SO /xM hypo-xanthine (H), 100 fiM PRibPP, and 1 mM MgCl2 in potassium phosphate (pH 7.4). At time intervals of 0 to 5 minutes, aliquots of the mixture were injected onto the HPLC ion-exchange column and eluted. Inset Time-dependent utilization of H and G and formation of GMP and IMP as determined by the absorbance of each peak at 254 nm. (From Ali and Sloan, 1982.)...

Further in vitro studies using a lung cancer cell line (A549) demonslrated that febuxostat (16 xM for 3h) completely inhibited xanthine oxidase activity without affecting the activities of adenosine deaminase, purine nucleoside phosphorylase, adenine phosphoribosyltransferase, hypoxanthine-guanine phosphoribosyltransferase, pyrimidine -nucleoside phosphorylase, or guanase. ... 

J. E. 1967. Xanthine phosphoribosyltransferase in man Relationship to hypoxanthine-guanine phosphoribosyltransferase. Biochem. Biophys. Res. Commun. 340-345. 

At the present time, we just report some experimental results of a study on the mechanism of action of allopurinol (U-hydroxy-pyrazolo (3, -d ) pyrimidine) and thiopurinol k thiopyrazolo (3, d) pyrimidine) on de novo biosynthesis of uric acid. In this present work, we have compared effect of alio and thiopurinol on oxypurine (xanthine and hypoxanthine) urinary excretion with their rate of synthesis of ribonucleotides in vitro by erythrocyte hemolysate in some particular enzymatic deficiencies (hypoxanthine-guanine phosphoribosyltransferase HGPRT, adenine phosphoribosyl-transferase APRT and xanthinuria). 

According to the experiments described in table 3 the addition of allopurinol does effect neither the inhibition of the hypoxanthine-guanine phosphoribosyltransferase by 6-MP nor the conversion of 6-MP to thioinosinic acid by the same enzyme. It is unprobable that this is due to a lack of xanthine oxidase in the cells investigated, because, in the same cell-free system the inhibitory effect of 6-MP on the formate activation was markedly increased by allopurinol (fig.6). 

Inosine formed by either route is then phosphorolyzed to yield hypoxanthine. Although, as we have previously seen, much of the hypoxanthine and guanine produced in the mammalian body is converted to IMP and GMP by a phosphoribosyltransferase, about 10% is catabolized. Xanthine oxidase, an enzyme present in large amounts in liver and intestinal mucosa and in traces in other tissues, oxidizes hypoxanthine to xanthine, and xanthine to uric acid (see fig. 23.20). Xanthine oxidase contains FAD, molybdenum, iron, and acid-labile sulfur in the ratio 1 1 4 4, and in addition to forming hydrogen peroxide, it is also a strong producer of the superoxide anion 02, a very reactive species. The enzyme oxidizes a wide variety of purines, aldehydes, and pteridines. 

Mbewe, B., Chibale, K., and McIntosh, D. B. (2007). Purification of human malaria parasite hypoxanthine guanine xanthine phosphoribosyltransferase (HGXPRT) using immobilized Reactive Red 120. Protein Expr. Purif. 52,153-158. 

Phosphoribosyltransferase activity was found for hypoxanthine, guanine and xanthine but not for adenine (2). Adenine and guanine deaminase activities are present. Phosphorylase activities were found for adenosine, guanosine and inosine. Also present were adenosine kinase and a guanosine phosphotransferase neither inosine kinase nor phosphotransferase activity was present. The IMP dehydrogenase differs from the mammalian enzyme in that it does not require for activity and it is more sensitive to inhibition by mycophenolic acid (13). 

Another approach followed by Wang et al. led to an inhibitor of Tritrichomonas foetus hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRT). The X-ray structure of this enzyme is available and it was used in a search for novel scaffolds. The Available Chemicals Directory (ACD) was screened with the program DOCK. Isatin and phthalic anhydride were capable of mimicking the substrate purine base and acting as competitive inhibitors. A virtual library of substituted... 

I. D. and Wang, C. (2000) Rational design of selective submicromolar inhibitors of Tritrichomonas foetus hypoxanthine-guanine-xanthine phosphoribosyltransferase. Biochemistry 39 4684-4691. 

Somoza JR, Chin MS, Focia PJ et al. Crystal structure of the hypoxanthine-guanine-xanthine phosphoribosyltransferase from the protozoan parasite Tritrichomonas foetus. Biochemistry 1996 35(22) 7032-7040. 

Figure 3. Compartmentalization of the purine salvage pathway of Leishmania. Abbreviations are as follows AAH, adenine aminohydrolase XPRT, xanthine phosphoribosyltransferase HGPRT, hypoxanthine-guaninephosphoribosyltransferase ADSS, adenylosuccinate synthetase ASL, adenylosuccinate lyase IMPDH, inosine monophosphate dehydrogenase GMPS, gua-nosine monophosphate synthase GDA, guanine deaminase AMPDA, adenosine monophosphate deaminase GMPR, guanosine monophosphate reductase APRT, adenine phosphoribosyltransferase AK, adenosine kinase. Enzymes that have been localized are shown in black and those that are predicted to be in the denoted locations are depicted in gray.

Hazleton KZ, Ho M, Cassera MB, Clinch K, Crump DR, Rosario I, Merino EF, Almo SC, Tyler PC, Schramm VL (2012) Acyclic immucillin phosphonates second-generation inhibitors of plasmodium falciparum hypoxanthine-guanine-xanthine phosphoribosyltransferase. Chem Biol 19 721-730... 

---