Uric acid complex

Xanthine dehydrogenase that mediates the conversion of hypoxanthine into xanthine and uric acid has been studied extensively since it is readily available from cow s milk. It has also been studied (Leimkiihler et al. 2004) in the anaerobic phototroph Rhodobacter capsulatus, and the crystal structures of both enzymes have been solved. Xanthine dehydrogenase is a complex flavoprotein containing Mo, FAD, and [2Fe-2S] redox centers, and the reactions may be rationalized (Hille and Sprecher 1987) ... 

Davies, K.J.A., Sevanian, A., Muakkassan-Kelly, S.F. and Hochstein, P. (1986). Uric acid-iron complexes. Biochem. J. 235, 747-754. 

Xanthine oxidoreductase (XOR) is a molybdenum-containing complex homodimeric 300-kDa cytosolic enzyme. Each subunit contains a molybdopterin cofactor, two nonidentical iron-sulfur centers, and FAD (89). The enzyme has an important physiologic role in the oxidative metabolism of purines, e.g., it catalyzes the sequence of reactions that convert hypoxanthine to xanthine then to uric acid (Fig. 4.36). 

Brydon and Roberts- added hemolyzed blood to unhemolyzed plasma, analyzed the specimens for a variety of constituents and then compared the values with those in the unhemolyzed plasma (B28). The following procedures were considered unaffected by hemolysis (up to 1 g/100 ml hemoglobin) urea (diacetyl monoxime) carbon dioxide content (phe-nolphthalein complex) iron binding capacity cholesterol (ferric chloride) creatinine (alkaline picrate) uric acid (phosphotungstate reduction) alkaline phosphatase (4-nitrophenyl phosphate) 5 -nucleotidase (adenosine monophosphate-nickel) and tartrate-labile acid phosphatase (phenyl phosphate). In Table 2 are shown those assays where increases were observed. The hemolysis used in these studies was equivalent to that produced by the breakdown of about 15 X 10 erythrocytes. In the bromocresol green albumin method it has been reported that for every 100 mg of hemoglobin/100 ml serum, the apparent albumin concentration is increased by 100 mg/100 ml (D12). Hemolysis releases some amino acids, such as histidine, into the plasma (Alb). 

A highly selective method for determination of lipid hydroperoxides is based on the oxidation of ferrocenecarboxylic acid (201) to the corresponding ferrocenium compound (202), as shown in equation 69, followed by amperometric reduction of this complex with a GCE set at —100 mV vs. SCSE, in phosphate buffer at pH 5.5. The method is insensitive to dissolved oxygen and no interference is observed, either from reductors such as ascorbic acid (22) or uric acid (29) nor from other hydroperoxides such as H2O2 and f-BuOOH at the 1 xM concentration level. At this concentration, a slight interference is observed for cumyl hydroperoxide (27) and 2-butanone peroxide (46 4- 47). The LOD... 

Colchicine, an alkaloid obtained from the autumn crocus, has long been used and is relatively selective for the treatment of acute gouty arthritis. Unlike many of the newer agents for use in gout, colchicine has minimal effects on uric acid synthesis and excretion it decreases inflammation associated with this disorder. It is thought that colchicine somehow prevents the release of the chemotactic factors and/or inflammatory cytokines from the neutrophils, and this in turn decreases the attraction of more neutrophils into the affected area (Fig. 37.1).The ability of colchicine to bind to leukocyte microtubules in a reversible covalent complex and cause their depolymerization also may be a factor in decreasing the attraction of the motile leukocytes into the inflamed area. 

Theophylline is 1,3-dimethylxanthine theobromine is 3,7-dimethylxanthine and caffeine is 1,3,7-trimethylxanthine. A theophylline preparation commonly used for therapeutic purposes is aminophylline, a theophylline-ethylenediamine complex. The clinical use of theophylline is discussed below. The metabolic products, partially demethylated xanthines (not uric acid), are excreted in the urine. 

Purine nucleotides are degraded by a pathway in which they lose their phosphate through the action of 5 -nucleotidase (Fig. 22-45). Adenylate yields adenosine, which is deaminated to inosine by adenosine deaminase, and inosine is hydrolyzed to hypoxanthine (its purine base) and D-ribose. Hypoxanthine is oxidized successively to xanthine and then uric acid by xanthine oxidase, a flavoenzyme with an atom of molybdenum and four iron-sulfur centers in its prosthetic group. Molecular oxygen is the electron acceptor in this complex reaction. 

Uric acid is found in the urine, blood, and muscle juices of carnivorous animals (herbivorous animals secrete hippuric acid), in the excrement of birds, serpents and insects, and is an oxidation product of the complex nitrogenous compounds of the animal organism. 

Most ultramicrobiosensors use differential measurement to overcome the problems of interferences and electrode fouling. The practical use of these biosensors for direct measurement is limited by interferents, such as ascorbic acid, acetaminophen (paracetamol), uric acid, etc., which are present in complex matricies such as serum. The specificity of the biochemical system is compromised by the partial selectivity of the electrode. The electrode not only oxidizes the desired product (e.g., H2O2 formed in the enzymatic oxidation of glucose by glucose oxidase), but also any other species oxidizable at the working potential. This produces a larger current response and a positive error. 

MnPc-SAMs have been employed for the detection of thiocyanate [86] on SAMs formed by coordination of MPc complexes to preformed SAMs. On MnPc-4-MPy-SAM the oxidation of SCN- occurred at 0.50 V (Table 3). The stability of the electrode was less on MnPc compared to CoPc preformed SAM. Analysis of SCN-in the presence of possible interfering species (uric acid, oxalic acid, and ascorbic acid) in biological samples revealed insignificant effects from these compounds [86], Thus, SCN- can be analyzed in the presence of ascorbic acid. An analysis of the urine of smokers and nonsmokers showed clearly that the SAM electrode could be used to differentiate between the two groups. 

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