Oxidase , aerobic xanthine

Nagano, T., and Fridovich, 1. (1985). The co-oxidation of ammonia to nitrite during the aerobic xanthine oxidase reaction. Arch. Bixhem. Biophys. 241, 596-601. 

Another route to the formation of H00./02. is UV irradiation of HOOH in aqueous solutions. Aerobic organisms produce minor fluxes of superoxide ion (02, and thereby HOO.) during respiration and oxidative metabolism for example, possibly up to 10-15% of the O2 reduced by cytochrome c oxidase and by xanthine oxidase passes through the H00./02. state. Thus, the chemistry of HOO. (and of 02 ) may be important to an understanding of oxygen toxicity in biological systems. In aprotic media, the rate of protonation of 02. is proportional to the acidity of the associated Bronsted acids (equation 96). Electrolytic oxidation of... 

Aerobic organisms produce minor fluxes of superoxide ion during respiration and oxidative metabolism. Thus, up to 15% of the O2 reduced by cytochrome-c oxidase and by xanthine oxidase passes through the HOO /O2 - state.70 The reductase of the latter system is a flavoprotein i that probably reduces O2 to HOOH via a redox cycle similar to that outlined by Eqs. (7-19) - (7-22). Thus, the observed flux of O2 -, which is the carrier of the auto-oxidation cycle, is due to leakage during turnover of xanthine/xanthine oxidase (see Scheme 7-14 for a reasonable mechanistic pathway). 

Aerobic P. d. The amino groups of adenine and guanine are removed hydrolytically by specific deaminases, which attack the free bases, the nucleosides or the nucleotides (Fig.). Uric acid is then produced by the action of xanthine oxidase (EC 1.2.3.2), which is the key enzyme of aerobic P.d. In humans and apes, the uric acid is excreted largely unchanged. In most reptiles and mammals, it is oxidized to allantoin by uricase (EC 1.73.3) (uricolysis). 

Xanthina oxidase, xanthine dehydrogenase, Schardtnger enzyme an enzyme of aerobic purine degradation, which catalyses the oxidation of hypoxan-thine to xanthine, and xanthine to uric acid Hypox-anthine + HjO + 62 -> Xanthine -h H2O2 Xanthine + H2O -H O2 -> Uric acid + H2O2. It is a dimeric enzyme, M, 275,000, pH-optimum 4.7, pi 5.35, containing 2 FAD, 2 Mo and 8 Fe (data for the enzyme from milk). The substrate specificity is low it catalyses the oxidation of other purines (e. g. adenine), aU-phatic and aromatic aldehydes, pyrimidines, pteri-dines and other heterocyclic compounds. 

Xanthine dehydrogenase (EC 1.1.1.204), the enzymatic precursor of xanthine oxidase (EC 1.1.3.22) reacts with doxorubicin via a two-electron reduction (Yee and Pritsos 1997). This reduction is different from the modified and more extensively studied form xanthine oxidase, which reacts with doxorubicin via a one-electron reduction. Under hypoxic conditions, the formation of large quantities of 7-deoxydoxorubicin aglycone, a deactivation product of doxorubicin metabolism, may serve to moderate the antineoplastic activity of doxorubicin. Under aerobic conditions, however, xanthine dehydrogenase activation led to a greater rate of formation of oxygen radicals than xanthine oxidase thereby possibty potentiating the cytotoxicity of doxorubicin to aerobic tumour cells. 

Models for monodithiolene molybdenum species related to xanthine oxidase and aerobic CODH have been described, e.g. [Mo(S2CgH4)02(SR)] [143]. The synthesis of related species with terminal sulfido ligands would enable assembly of the indicated (dithiolene)Mo02S-CuSR ensembles. The interaction of M0S4 and Cu has received considerable study, motivated by interest in the ability of dietary Mo to inhibit copper uptake in ruminants [144]. Bi-, tri-, tetra-, or higher nuclearity Cu-Mo clusters result from the reaction of MoS and Cu" in the presence of tertiary phosphines, amines, or cyanide [144]. 

Free radical reactions are necessary for the normal operation of a number of biological processes. The catalytic action of many enzymes such as xanthine oxidase and electron transport processes involves one-electron transfers that yield free radical intermediates. Because of the ubiquity of molecular oxygen in aerobic organisms and... 

It is the coenzyme of xanthine oxidase, aldehyde oxidase and other aerobic dehydrogenases. Like riboflavin and FMN, FAD is universally present in the biosphere. It is reddish-yellow in colour but, like FMN and riboflavin, its solutions are a yellow-green. 

There is another type of oxidative process which might be classified among the energizing reactions. The first step in the oxidation of tryptophan to formyl kynurenine is catalyzed by a peroxidase-H202 system.Aerobic oxidases such as xanthine oxidase, d-amino acid oxidase, and urico-oxidase produce H2O2 during oxidation of their respective... 

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