Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.17.3.2 (xanthine oxidase)
 8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Eosinophil and/or neutrophil leukocytes appear to have important roles in host defense against invasive, migratory helminth infestations, but the mechanisms of larval killing by leukocytes are uncertain. This study examines killing of newborn (migratory phase) larvae of Trichinella spiralis during incubation with granule preparations of human eosinophils or neutrophils and generators of hydrogen peroxide (glucose-glucose oxidase) (G-GO) or superoxide and hydrogen peroxide (xanthine-xanthine oxidase). Larvae were killed by either hydrogen peroxide-generating system in a concentration-dependent manner. Direct enumeration of surviving larvae after incubation in microtiter wells containing the appropriate reagents was used in assess larval killing. Verification of the microplate assay was demonstrated by complete loss of larval ability to incorporate [(3)H]deoxyglucose and loss of infectivity after incubation in comparable concentrations of G-GO. Larvae were highly sensitive to oxidative products; significant killing occurred after incubation with 0.12 mU glucose oxidase and complete killing occurred with 0.5 mU. Comparable killing of bacteria required over 60 mU glucose oxidase. At 5 mU glucose oxidase, killing was complete after 6 h of incubation. Killing by G-GO was inhibited by catalase but not by boiled catalase or superoxide dismutase and was enhanced by azide. Addition of peroxidase in granule pellet preparations of eosinophils or neutrophils did not enhance killing by G-GO. These data indicate a remarkable susceptibility of newborn larvae of T. spiralis to the hydrogen peroxide generated by neutrophil and eosinophil leukocytes.
J Clin Invest 1979 Dec
PMID:Mechanisms of killing of newborn larvae of Trichinella spiralis by neutrophils and eosinophils. Killing by generators of hydrogen peroxide in vitro. 4 Oct 2

A molybdenum cofactor (Mo-co) from xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) can be isolated from the enzyme by a technique that has been used to isolate an iron-molybdenum cofactor (FeMo-co) from component I of nitrogenase. N-Methylformamide is used for the extraction of these molybdenum cofactors. Mo-co from xanthine oxidase activates nitrate reductase (NADPH:nitrate oxidoreductase, EC 1.6.6.2) in an extract from Neurospora crassa mutant strain Nit-1; however, FeMo-co is unable to activate nitrate reductase in strain Nit-1. Mo-co from xanthine oxidase is unable to activate nitrogenase in an extract of Azotobacter vinelandii mutant strain UW45. Inactive component I in this extract can be activated by FeMo-co. These results indicate that nitrate reductase and xanthine oxidase share a common molybdenum cofactor, but this cofactor is different from the molybdenum cofactor in nitrogenase.A. vinelandii synthesizes both Mo-co and FeMo-co. Mo-co is produced when the cells fix N(2) and also when they are repressed for nitrogenase synthesis by growth in a medium containing excess ammonium. However, FeMo-co is not produced when cells are grown in an ammonium-containing medium. Partially purified preparations of component I from A. vinelandii and Klebsiella pneumoniae contain both FeMo-co and Mo-co. The presence of both FeMo-co and Mo-co activities in partially purified preparations of component I explains previous reports of activation of inactive nitrate reductase in strain Nit-1 by acid-treated component I of nitrogenase. The Mo-co can be separated from FeMo-co in these preparations by chromatography on Sephadex G-100 in N-methylformamide. Both FeMo-co and Mo-co are sensitive to oxygen.
Proc Natl Acad Sci U S A 1977 Dec
PMID:Molybdenum cofactors from molybdoenzymes and in vitro reconstitution of nitrogenase and nitrate reductase. 14 98

The behavior of the rate-limiting enzyme of purine catabolism, xanthine oxidase (EC 1.2.3.2); was examined in normal liver, in 17 hepatomas of different growth rates, and in rapidly growing differentiating and regenerating liver. Xanthine oxidase activity was measured in the supernatant fluid prepared by centrifugation of 5% homogenates at 100,000 X g for 30 min. There was no uricase activity in the supernatant fluid. The affinity of xanthine oxidase to xanthine was similar in normal liver and in slow- and rapidly growing hepatomas (Km=6 to 8 muM), and theoptimum pH was 8.0; at pH 7.4, the activity was 80% of that at the pH optimum. A standard assay was worked out for the liver and hepatoma systems; the enzyme activity was linear during 60-min incubation and proportionate with amounts of protein added over a range of 0.5 to 3.0 mg. Xanthine oxidase specific activity was 9 times higher in small intestine than in liver. Activities in lung, spleen, kidney, heart, testes, and thymus were 67, 59, 21, 19, 8, and 8%, and in skeletal muscle, brain, and bone marrow activities were 5% of that of the liver. In regenerating liver, xanthine oxidase activity was not changed from that of the liver of sham-operated controls up to 96 hr after operation. The activity of the average differentiating liver cell was less than 5% of that of adult liver during the first week after birth. At postnatal ages of 18, 25, 30 and 40 days, the activity rose to 18, 46, 76, and 94%, respectively, of that of the adult liver. In starvation, hepatic xanthine oxidase activity per cell was preferentially depleted as compared to the decline in protein concentration. Upon refeeding, the enzymatic activity was restored more slowly than the protein content. Since xanthine oxidase activity was decreased in all examined hepatomas, including the slowest-growing, well-differentiated neoplasms, the altered activity of this enzyme appears to be.linked with neoplastic transformatiobosyl 1-pyrophosphate amidotransferase (EC 2.4.2.14), was increassed in the hepatomas, the reprogramming of gene expression results in an imbalance that favors the synthetic over the catabolic potential. This enzymatic imbalance should confer selective advantages to the cancer cells.
Cancer Res 1976 Dec
PMID:Imbalance of purine metabolism in hepatomas of different growth rates as expressed in behavior of xanthine oxidase (EC 1.2.3.2). 18 29

The electron-spin relaxation of iron-sulphur centres in a range of simple proteins (ferredoxin, high-potential iron-sulphur protein and rubredoxin) was investigated by means of the temperature dependence and microwave power saturation of the EPR signal. The proteins containing [2Fe-2S] centres all showed temperature optima higher than those for [4Fe-4S] centres, but the difference between the slowest-relaxing [4Fe-4S] protein (Chromatium high-potential iron-sulphur protein) and the fastest-relaxing [2Fe-2S] protein (Halobacterium halobium ferredoxin) was small. A greater distinction was seen in the power saturation behaviour at low temperature (10--20 K). The behaviour of the signal intensity as a function of microwave power was analyzed in terms of the power for half saturation P 1/2 and the degree of homogeneous/inhomogeneous broadening. The effect of distorting the protein structure by salts, organic solvents and urea was to decrease the electron-spin relaxation rate as shown by a decreased value of P 1/2. The addition of Ni2+ as a paramagnetic perturbing agent caused an increase in the electron-spin relaxation rate of all the proteins, with the exception of adrenal ferredoxin, as shown by an increased P 1/2 and, in a few cases, broadening of the linewidth. Ferricyanide, a commonly used oxidizing agent, has similar effects. These results are discussed in relation to the use of paramagnetic probes to determine whether iron-sulphur centres are near to a membrane surface. Spin-spin interactions between two paramagnetic centres in a protein molecule such as a 2[4Fe-4S] ferredoxin, lead to more rapid electron-spin relaxation. This method was used to detect a spin-spin interaction between molybdenum V and centre Fe-SI in xanthine oxidase.
Biochim Biophys Acta 1978 Dec 20
PMID:Electron spin relaxation of iron-sulphur proteins studied by microwave power saturation. 21 17

The observation by Bray & Knowles [Proc. R. Soc. London Ser. A (1968) 302, 351--353] of direct transfer, during the catalytic reaction, of hydrogen atoms from substrate molecules to the enzyme xanthine oxidase was reinvestigated. The experimental phenomenon and its basic interpretation were confirmed and extended. In the reduced functional enzyme, molybdenum(V) interacts with two enzyme-bound protons, which are exchangeable with solvent protons. One of these is coupled to the metal with AHav. 1.4mT and the other with AHav. 0.3mT. The molecule also contains a site for the binding of anions, presumably as ligands of molybdenum. This is shown by effects of nitrate ions on the e.p.r. spectra. The spectra of the nitrate and 1-methylxanthine complexes of the reduced enzyme are very similar to one another, and are designated Rapid type-1 spectra. It is concluded that, in the Michaelis complex, the substrate molecule occupies the anion site, probably being bound to molybdenum via the nitrogen in its 9-position. During the turnover process, hydrogen from the substrate C-8 position, after transfer to the enzyme, appears as the proton more strongly coupled to molybdenum. This proton then exchanges with solvent deuterium with a rate constant of 27s-1, at pH 8.2 and 12 degrees C. It has been confirmed that substrate molecules occupying the anion site do not interfere with observation of the transfer and exchange processes.
Biochem J 1978 Dec 01
PMID:The molybdenum centre of native xanthine oxidase. Evidence for proton transfer from substrates to the centre and for existence of an anion-binding site. 21 53

The non-functional form of xanthine oxidase known as the desulpho enzyme was compared with the functional enzyme in various ways, to obtain information on the structure of the molybdenum centre and the mechanism of the catalytic reaction. The desulpho enzyme, like the functional one, possesses a site for the binding of anions, presumably as ligands of molybdenum. Evidence is presented that in the Mo(V) e.p.r. signal from the desulpho-enzyme, as in that from the functional enzyme, a weakly coupled proton, in addition to a strongly coupled proton, interacts with the metal. Measurements were carried out by e.p.r. on the rate at which the proton strongly coupled to molybdenum exchanged, on diluting enzyme samples with 2H2O. For the desulpho enzyme the exchange rate constant was 0.40s-1, at pH 8.2 and 12 degrees C, and for the functional enzyme it was 85 s-1. It is shown that the great majority of reported differences between the enzyme forms are consistent with functional enzyme containing an (Enzyme)-Mo=S grouping, replaced in the desulpho form by (Enzyme)-Mo=O. Protonation of these groups, with pK values of about 8 and 10 respectively, would give (Enzyme)-Mo-SH and (Enzyme)-Mo-OH, these being the forms observed by e.p.r. The accepting group in the functional enzyme, for the proton transferred from the substrate while molybdenum is reduced in the catalytic reaction [Gutteridge, Tanner & Bray (1978) Biochem J. 175 869-878], is thus taken to be Mo=S.
Biochem J 1978 Dec 01
PMID:Comparison of the molybdenum centres of native and desulpho xanthine oxidase. The nature of the cyanide-labile sulphur atom and the nature of the proton-accepting group. 21 54

Xanthine oxidase suffers autoinactivation in the course of catalyzing the oxidation of acetaldehyde. When no special efforts were made to maintain a high pO2 in these reaction mixtures catalase protected the xanthine oxidase, but superoxide dismutase did not. However, when oxygen depletion was slowed or prevented by working at lower concentrations of xanthine oxidase, at lower temperatures or by vigorous agitation under an atmosphere of 100% oxygen, superoxide dismutase or catalase protected markedly when added separately and protected almost completely when added together. This result correlates with the greater production of O2-, relative to H2O2, by xanthine oxidase, at elevated pO2. Since histidine also provided some protection and the high levels of acetaldehyde used would have precluded any significant effect of OH., we conclude that singlet oxygen, or something with similar reactivity, was generated from O2- plus H2O2 and contributed significantly to the observed autoinactivation.
Biochim Biophys Acta 1979 Dec 07
PMID:Autoinactivation of xanthine oxidase: the role of superoxide radical and hydrogen peroxide. 22 31

Methane (CH(4)) production from the anti-inflammatory agent, dimethyl sulfoxide (DMSO), was used to measure .OH from chemical reactions or human phagocytes. Reactions producing .OH (xanthine/xanthine oxidase or Fe(++)/EDTA/H(2)O(2)) generated CH(4) from DMSO, whereas reactions yielding primarily O-(2) or H(2)O(2) failed to produce CH(4). Neutrophils (PMN), monocytes, and alveolar macrophages also produced CH(4) from DMSO. Mass spectroscopy using d(6)-DMSO showed formation of d(3)-CH(4) indicating that CH(4) was derived from DMSO. Methane generation by normal but not chronic granulomatous disease or heat-killed phagocytes increased after stimulation with opsonized zymosan particles or the chemical, phorbol myristate acetate. Methane production from DMSO increased as the number of stimulated PMN was increased and the kinetics of CH(4) production approximated other metabolic activities of stimulated PMN. Methane production from stimulated phagocytes and DMSO was markedly decreased by purportedly potent .OH scavengers (thiourea or tryptophane) and diminished to lesser degrees by weaker .OH scavengers (mannitol, ethanol, or sodium benzoate). Superoxide dismutase or catalase also decreased CH(4) production but urea, albumin, inactivated superoxide dismutase, or boiled catalase had no appreciable effect. The results suggest that the production of CH(4) from DMSO may reflect release of .OH from both chemical systems and phagocytic cells. Interaction of the nontoxic, highly permeable DMSO with .OH may explain the anti-inflammatory actions of DMSO and provide a useful measurement of .OH in vitro and in vivo.
J Clin Invest 1979 Dec
PMID:Generation of hydroxyl radical by enzymes, chemicals, and human phagocytes in vitro. Detection with the anti-inflammatory agent, dimethyl sulfoxide. 50 Aug 30

In a 3-week old female child with clinical features including neurologic abnormalities and lens dislocation, xanthinuria co-existed with increased excretion of sulfur compounds (sulfite, S-sulfocysteine, taurine and thio-sulfate). Low xanthine oxidase and absent sulfite oxidase activities were found on liver biopsy. No abnormality was detected in either parent. Both the above enzymes are molybdenum-flavoproteins. Normal serum molybdenum concentration seemed to rule out dietary deficiency or impaired absorption. A defect in the incorporation of the metal into flavoproteins is postulated in this case.
Clin Biochem 1979 Dec
PMID:Simultaneous occurrence of xanthine oxidase and sulfite oxidase deficiency. A molybdenum dependent inborn error of metabolism? 58 2

Until recently there were no reports regarding the presence of xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) in plants. Direct evidence for its presence in lentil seedlings is reported here. Xanthine oxidase activity increases with the period of germination, reaching a maximum at 24 h and decreasing thereafter. The pH optimum for its activity is at pH 8.0. Almost equal activity is observed against xanthine and hypoxanthine. The Km for xanthine is 1.05 mM, and considerable inhibition is observed at high substrate concentration.
Biochim Biophys Acta 1977 Dec 08
PMID:Xanthine oxidase in lentil (Lens esculenta) seedlings. 92 22


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