Xanthines uric acids

Anti-gout Drugs. Figure 1 Xanthine oxidase-catalyzed reactions. Xanthine oxidase converts hypoxanthine to xanthine and xanthine to uric acid, respectively. Hypoxanthine and xanthine are more soluble than uric acid. Xanthine oxidase also converts the uricostatic drug allopurinol to alloxanthine. Allopurinol and hypoxanthine are isomers that differ from each other in the substitution of positions 7 and 8 of the purine ring system. Although allopurinol is converted to alloxanthine by xanthine oxidase, allopurinol is also a xanthine oxidase inhibitor. Specifically, at low concentrations, allopurinol acts as a competitive inhibitor, and at high concentrations it acts as a noncompetitive inhibitor. Alloxanthine is a noncompetitive xanthine oxidase inhibitor. XOD xanthine oxidase. 

G. Dryhurst and co-workers have investigated the electrochemistry of naturally occurring JV-heterocyclic molecules, including uric acid, xanthine, adenine, and guanine,5,402 in the expectation that the mechanisms observed electrochemically might lead to a more detailed understanding of the biological redox reactions of these molecules. 

NAD+. They catalyze the hydroxylation of purines. Equation (50) shows the xanthine oxidase-catalyzed oxidation of xanthine to uric acid. Xanthine oxidase is probably the most well-studied molybdenum enzyme. There is good evidence that the molybdenum is the site for binding and reduction of xanthine. The enzyme contains MoVI in the resting form, while MoIV and Mov are implicated during catalysis. 

Plasma Diabetes without nephropathy, diabetic nephropathy III, IV, and V Healthy subjects 50 patients 88 HPLC-UV- MS/MS Adenosine, inosine, uric acid, xanthine, and creatinine (44)... 

Xanthine oxidase catalyzes the oxidation of hypox-anthine and xanthine to uric acid. Xanthine oxidase is a complex metalloflavoprotein containing one molybdenum, one FAD and two iron-sulfur centers of the ferredoxine type in each of its two independent subunits. Usually, the enzyme is isolated from cow s milk. The enzyme is inhibited by allopurinol and related compounds. The production of uric acid from the substrate (xanthine) can be determined by measuring the change in optical density in the UV range. 

PURINE DERIVATIVES ALLANTOIN, URIC ACID, XANTHINE, AND HYPOXANTHINE... 

RP-HPLC procedures for the determination of creatinine and purine metabolites, such as allantoin, uric acid, xanthine, and hypoxanthine in ruminant urine, were described. Chromatography was achieved with a Cig column under isocratic conditions, and detection at 218 nm without allantoin derivatization. The chromatographic conditions were a compromise between the sensitivity and specificity of the measurement of each analyte, analysis time, and resolution of all analyte peaks from interfering compounds.Uremic toxins creatine, creatinine, uric acid, and xanthine were simultaneously determined in human biofluids, simply after dilution, with UV detection at 200 nm. This method was compared, for creatinine and uric acid, with conventional routine methods and did not give significantly different results. 

Czaudema, M. Kowalczyk, J. Quantification of allantoin, uric acid, xanthine and hypoxanthine in ovine urine by high-performance liquid chromatography and photodiode array detection. J. Chromatogr., B 2000, 744, 129-138. 

Purines are metabolized in a series of reactions involving hypoxanthine, xanthine, uric acid, and allantoin as end products that are subsequently excreted in urine. Fig. 3 shows the metabolic pathways for xanthine. Measurement of urinary excretion of purine metabolites, primarily allantoin or, additionally, uric acid, xanthine, and hypoxanthine, has been proposed as a marker for microbial... 

Other metabolites that have been measured with thermistor-based biosensors include ascorbic acid, cephalosporins, creatinine, galactose, hydrogen peroxide, lactose, malate, phospholipids, uric acid, xanthine, and hypoxanthine. 

Simultaneous antipyrine, caffeine, 8-chlorotheophylline, dimethyluric acid, dyphylline, hjrpoxanthine, methyluric acid, methylxanthine, pentifylline, phenacetin, 8-phenyltheo-phyUine, theobromine, uric acid, xanthine Interfering pentobarbited... 

Simultaneous caffeine, hypoxanthine, propentofylline, theobromine, theophylline, uric acid, xanthine... 

As one would expect, since these patients owe their overproduction of uric acid to excessive release of hypoxanthine, they often do not respond well to allopurinol unless great care is taken in adjusting the dose. These patients, like Lesch-Nyhan patients, have limited ability to anabolize hypoxanthine to inosinate. Production of xanthine, which is no more soluble than uric acid, is not to the patients advantage (K15). Proper regulation of the allopurinol results in a beneficial distribution of the purines into three products, uric acid, xanthine, and hypoxanthine and resolves the solubility problem. 

Isotachophoresis has already been successfully applied to the analysis of urine of persons exposed to styrene, toluene, and xylene, for the contents of mandelic, phenylglyoxylic, hippuric and methylhippuric acids . For the clinical disgnostic of inborne metabolic disorders of purines and pyrimidines, it has been elaborated permitting the identification of different inborne disorders of the metabolism of these bases by the contents of characteristic metabolites excreted in urine (adenine, uric acid, xanthin, deoxyinosin, deoxyguanosin etc.). 

Nitrogen compounds acetylcholine, aminopyrine, aniline, bilirubin, cadaverine, caprolactam, epinephrine, guanosine, hypoxanthine, inosine, lecithin, monoamines, penicillin, spermine, spermidine, theophylline, urea, uric acid, xanthine. 

Fischer (1884) recognised that uric acid, xanthine, and hypoxanthine are oxides of a hypothetical base C5N4H4, which he called purine from purum and uricum) ... 

Cai, X., Kalcher, K., and Neuhold, C. (1994) Simultaneous determination of uric acid, xanthine and hypoxanthine with an electrochemically pretreated carbon paste electrode. Fresenius ). Anal. Chem., 348, 660-665. 

Purine bases are a group of compounds found in plants and animals —they include nucleic acids. Their biosynthesis is complex with numerous non-amino-acid precursors (Samuelsson 1992). Xanthine, an oxidised purine that occurs as a breakdown product of nucleic acid metabolism, is itself oxidised in the body to uric acid. Xanthine consists of two fused ring systems each containing two nitrogen atoms. 

Allantoin, uric acid, xanthine, and hypoxanthine were extracted fixrm ruminant blood and urine. Samples were treated with and without DNPH [2,4-dintriphenyIhy-drazine) prior to analysis to derivatize the allantoin. Two 25 cm C g columns were cormected in series (A = 205 nm and 254 nm for nonderivatized sample 254 nm and 360 nm for derivatized sample). A complex 45-min 100/0 80/20 water (2.5 mM... 

---