Oxidation uric acid

Canellakis ES, PP Cohen (1955) The end-prodncts and intermediates of uric acid oxidation by nricase. J Biol Chem 213 385-395. 

The problem of selectivity is the most serious drawback to in vivo electrochemical analysis. Many compounds of neurochemical interest oxidize at very similar potentials. While this problem can be overcome somewhat by use of differential waveforms (see Sect. 3.2), many important compounds cannot be resolvai voltammetrically. It is generally not possible to distinguish between dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) or l tween 5-hydroxytryptamine (5-HT) and 5-hydroxyindolacetic acid (5-HIAA). Of even more serious concern, ascorbic acid oxidizes at the same potential as dopamine and uric acid oxidizes at the same potential as 5-HT, both of these interferences are present in millimolar concentrations... 

Parks, D.A., Tan, S., Poplawski, S.C., Baldwin, S. and Sweeney, S.D. (1992). Uric acid oxidation products indicator of oxidant stress in human liver transplantation. Gastroenterology 102, A232. 

Fichter and Kern O first reported that uric acid could be electrochemically oxidized. The reaction was studied at a lead oxide electrode but without control of the anode potential. Under such uncontrolled conditions these workers found that in lithium carbonate solution at 40-60 °C a yield of approximately 70% of allantoin was obtained. In sulfuric acid solution a 63% yield of urea was obtained. A complete material balance was not obtained nor were any mechanistic details developed. In 1962 Smith and Elving 2) reported that uric acid gave a voltammetric oxidation peak at a wax-impregnated spectroscopic graphite electrode. Subsequently, Struck and Elving 3> examined the products of this oxidation and reported that in 1 M HOAc complete electrochemical oxidation required about 2.2 electrons per molecule of uric acid. The products formed were 0.25 mole C02,0.25 mole of allantoin or an allantoin precursor, 0.75 mole of urea, 0.3 mole of parabanic acid and 0.30 mole of alloxan per mole of uric acid oxidized. On the basis of these products a scheme was developed whereby uric acid (I, Fig. 1) is oxidized in a primary 2e process to a shortlived dicarbonium ion (Ha, lib, Fig. 1) which, being unstable, under-... 

Uric acid is one of the principal products of purine metabolism in man 12 13). However, in many other organisms further oxidative degradation of the purine molecule occurs. One of the most important enzymes involved in uric acid oxidation is uricase, which has been studied to some extent in vitro. 

AUantoin, uric acid oxidation, 625 AUene hydroperoxides, regioselectivity with twisted 1,3-dienes, 856-7, 858 Allen s reagent... 

Santos, C. X. C., Anjos, E. I., and Augusto, O., Uric acid oxidation by peroxynitrite Multiple reactions, free radical formation, and amplification of lipid oxidation. Arch. Biochem. Biophys. 372, 285-294 (1999). 

The activity of deflavo-bovine XO (lacking the FAD cofactor) was demonstrated by deliberate removal of the FAD cofaetor (with CaCl2). Deflavo bovine XO still exhibited the ability to oxidize hypoxanthine to xanthine using dimethylferrocenium as the mediator. This parallels the urie aeid mediated electrocatalysis of (partially) deflavo K capsulatus XDH mentioned above. For the bovine XO enzyme, data were also reported for the dimethylferrocenium mediated oxidation of xanthine but it is not clear whether this eat-alytic current was convoluted with uric acid oxidation (at a similar potential... 

A large number of products, including some of the products of uricase action, are produced from uric acid by peroxidases + enzymatically generated H202. The nonspecific action of peroxidases emphasizes the part played by nonenzymatic reactions of the unstable products of uric acid oxidation. 

Oxidation of Uric Acid.—Oxidation of uric acid in alkaline solution opens up the pyrimidine ring, producing allantoin. Oxidation in acid solution opens up the iminazole ring, producing alloxan. 

In mature nodules of both types only about 60% of the cells contain bacteroids, the other remain uninfected (Dart, 1977). While the role of uninfected cells in indeterminate nodules is unknown, uninfected cells of determinate, spherical nodules that form ureides are the site of uric acid oxidation to form aJlantoin and allantoic acid (Newcomb and Tandon, 1981 Newcomb et al, 1985 Schubert, 1986). Isolated uninfected cells from soybean and French bean have high uricase activity as compared to infected cells. In addition, immunocytochemical techniques demonstrated that uricase was located in the peroxisomes of uninfected cells of soybean nodules (Verma et al, 1986). 

The presence of this enzyme in seedlings has long been known (Fosse et al., 1929a, 1930 Gayrel, 1959). The seedling enzyme has been localized in glyoxi-somes in seven different species (Theimer and Beevers, 1971). Preparations of these particles from Ricinus communis catalyzed uric acid oxidation with a pH optimum of 8.9 and a for uric acid of0.007 mM. High concentrations of uric acid were inhibitory, as were xanthine, hypoxanthine, and adenine. 

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