Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

A previously unidentified fraction lacking xanthine:O2 activity has been isolated during affinity chromatography of bovine milk xanthine oxidase preparations on Sepharose 4B/folate gel. Unlike active, desulfo, or demolybdo forms of xanthine oxidase, this form, which typically comprises about 5% of an unfractionated enzyme solution, passes through the affinity column without binding to it, and is thus easily separated from the other species. The absorption spectrum of this fraction is very similar to that of the active form, but has a 7% lower extinction at 450 nm. Analysis of the fraction has shown that it is a dimer of normal size, but that it does not contain molybdenum or molybdopterin (MPT). The "MPT-free" xanthine oxidase contains 90-96% of the Fe found in active xanthine oxidase, and 100% of the expected sulfide. EPR and absorption difference spectroscopy indicate that the MPT-free fraction is missing approximately half of its Fe/S I centers. The presence of a new EPR signal suggests that an altered Fe/S center may account for the nearly normal Fe and sulfide content. Microwave power saturation parameters for the Fe/S II and Fe/S I centers in the MPT-free fraction are normal, with P1/2 equal to 1000 and 60 mW, respectively. The new EPR signal shows intermediate saturation behavior with a P1/2 = 200 mW. The circular dichroism spectrum of the MPT-free fraction shows distinct differences from that of active enzyme. The NADH:methylene blue activity of the MPT-free fraction is the same as that of active xanthine oxidase which exhibits xanthine:O2 activity, but NADH:cytochrome c and NADH:DCIP activities are diminished by 54 and 37%, respectively.
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PMID:A molybdopterin-free form of xanthine oxidase. 282 75

In a recent publication [(1987) FEBS Lett. 210, 195-198] the authors claim the use of cytochrome c to detect superoxide anion underestimates the real rate of superoxide anion formation on the basis that: (i) the rate of uric acid formation by xanthine oxidase is about 4-fold faster than the rate of cytochrome c reduction and (ii) hydrogen peroxide formed upon dismutation of the superoxide anion generated by xanthine oxidase is capable of reoxidizing ferrocytochrome c. That paper may have been misleading for readers not very familiar with the field of oxygen radicals, since both assumptions are, in fact, incorrect. In this report we demonstrate that the build up in concentration of H2O2 during most reactions in which superoxide anion is being produced is not enough to affect the rate of cytochrome c reduction. Our results suggest that the authors may have been misled by an artifact due to exposure of the samples containing H2O2 to UV light, which generates hydroxyl radicals by photolysis.
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PMID:How relevant is the reoxidation of ferrocytochrome c by hydrogen peroxide when determining superoxide anion production? 282 12

Cytochrome a1c1 (nitrite-cytochrome c oxidoreductase) purified from Nitrobacter winogradskyi (formerly N. agilis) contained molybdenum, non-heme iron, and acid-labile sulfur in addition to hemes a and c; it contained 1 mol of heme a, 4-5 g atoms of non-heme iron, 2-5 g atoms of acid-labile sulfur, and 1-2 g atoms of molybdenum per mol of heme c, but did not contain copper. The fluorescence spectra of the molybdenum cofactor derivative prepared from cytochrome a1c1 were very similar to those of the cofactor derivative from xanthine oxidase, and the aponitrate reductase of nit-1 mutant of Neurospora crassa was complemented by addition of the molybdenum cofactor derived from the cytochrome. Further, the ESR spectrum of cytochrome a1c1 was similar to that of liver sulfite oxidase. The content of cytochrome a1 in the cells cultivated with the medium in which tungsten was substituted for molybdenum markedly decreased as compared with that in the cells cultivated in the molybdenum-supplemented medium. These results indicate that cytochrome a1c1 is an iron-sulfur molybdoenzyme which contains hemes a and c.
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PMID:Nitrobacter winogradskyi cytochrome a1c1 is an iron-sulfur molybdoenzyme having hemes a and c. 282 43

Uroporphyrin I, haematoporphyrin and haematoporphyrin derivative had no effect on O2-. generation during oxidation of hypoxanthine by xanthine oxidase and on the formation of hydroxyl radicals (OH.) in the hypoxanthine/xanthine oxidase/Fe3+-EDTA/deoxyribose system. On the other hand, these porphyrins strongly inhibited O2-. formation in a horseradish peroxidase/H2O2/NADPH mixture, whereas they augmented OH. generation in this system after addition of Fe3+-EDTA. Experimental evidence suggests that these observations should be ascribed to the formation of a porphyrin anion radical in the horseradish peroxidase/NADPH system. The formation of this anion radical was confirmed by e.s.r. spectroscopy. This radical is apparently unable to reduce cytochrome c, but it can replace O2-. in the OH.-generating Haber-Weiss reaction.
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PMID:The influence of porphyrins on iron-catalysed generation of hydroxyl radicals. 283 35

Methylene blue competes 100 to 600 times more effectively than paraquat for reduction by three different flavo-containing enzymes; xanthine oxidase, NADH cytochrome c reductase, and NADPH cytochrome c reductase. Paraquat and methylene blue both interact with deflavo xanthine oxidase, indicating that neither electron acceptor reacted at the FAD site of the enzyme where molecular oxygen is reduced to superoxide. As the paraquat radical also directly reduced acetylated cytochrome c the hemeprotein could not be utilized for measuring superoxide production in the presence of the herbicide. In the presence of cytochrome c the methylene blue caused a sharp decrease in both paraquat-induced superoxide and hydroxyl radical production.
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PMID:Methylene blue competes with paraquat for reduction by flavo-enzymes resulting in decreased superoxide production in the presence of heme proteins. 283 6

The detergent-induced amplification of lucigenin-dependent chemiluminescence of O2-, generated by xanthine oxidase or microsomal NADPH oxidase was studied. An assay system is described which is at least 10 times more sensitive than normal lucigenin-dependent chemiluminescence due to the amplification by high concentrations of octylphenylpolyethylene glycol (Triton X-100). Compared to the superoxide dismutase-sensitive reduction of acetylated cytochrome c, a 3750-fold lower amount of microsomal protein was necessary to produce an O2- signal 10-fold above the background. In contrast to cytochrome c reduction, detergent-amplified chemiluminescence of lucigenin was completely inhibited by superoxide dismutase and therefore more selective for O2-. The membrane-bound and Triton X-100-solubilized NADPH oxidase from microsomes of macrophages was activated by ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid and inhibited by Ca2+ and sodium dodecyl sulfate. The membrane-bound enzyme showed a Km value of 1.35 microM, which decreased to 0.95 microM after the addition of 12% (g/g) Triton X-100. The Km and Vmax values of soluble xanthine oxidase were not influenced by Triton X-100, indicating that the enzyme activities were not impaired by the high concentrations of detergent.
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PMID:Detergent-amplified chemiluminescence of lucigenin for determination of superoxide anion production by NADPH oxidase and xanthine oxidase. 283 20

To determine whether the effects of endotoxin on cultured lung endothelium involve proteolytic mechanisms, we incubated bovine pulmonary arterial endothelial cells with endotoxin in medium 199 + 10% fetal bovine serum (FBS) in the presence and absence of several proteinase inhibitors. Three chloromethyl ketone (CK) derivatives [N-tosyl-L-lysine (CK)-(TLCK), N-tosyl-L-phenylalanine CK(TPCK), methoxysuccinyl-Ala-Ala-Pro-Val CK(SPCK)] and a single synthetic proteinase substrate [N-alpha-p-tosyl-L-arginine methyl ester hydrochloride (TAME)] attenuated endotoxin-induced cytotoxicity (lactate dehydrogenase release) and prostacyclin production in a dose-related fashion. The most effective inhibitors of endotoxin-induced cytotoxicity were TLCK and TPCK. TLCK and TAME most effectively attenuated endotoxin-stimulated prostacyclin production. Two chemically unrelated substances, soybean trypsin inhibitor and alpha 1 proteinase inhibitor also attenuated the endotoxin response. In the absence of FBS or in the presence of 10% heat-inactivated FBS, antiproteases attenuated endotoxin-induced prostacyclin production but had less effect on cytotoxicity than with 10% FBS. We also measured the capacity of the CK inhibitors to scavenge superoxide radicals generated in a cell-free xanthine/xanthine oxidase system by measuring inhibition of cytochrome c reduction. Percent scavenging of superoxide by these inhibitors was as follows: TLCK, 62.7 +/- 5.8 (SE); TPCK, 83.9 +/- 7.7; TAME, 24.5 +/- 6.4; SPCK, 0. We conclude that certain proteinase inhibitors attenuate endotoxin-induced endothelial cytotoxicity and prostacyclin production and that direct scavenging of superoxide radicals fails to explain the protective effects of proteinase inhibition. We speculate that the effects of endotoxin on lung endothelium may involve proteolytic mechanisms even in the absence of neutrophils.
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PMID:Antiproteinases protect cultured lung endothelial cells from endotoxin injury. 284 19

We postulated that Captopril may be capable of acting as a scavenger of free radicals, and performed in vitro studies using harvested human neutrophils. We studied the effect of Captopril on the reduction of Fe3+ cytochrome c by stimulated PMN's. Captopril acts as a reducing agent in this system, and is capable of reducing Fe3+ cytochrome c by itself. NADPH oxidase was harvested from PMA-stimulated human PMN's. Captopril inhibited the activity of this enzyme as assessed by the disappearance of NADPH determined spectrophotometrically. Since similar inhibition could be demonstrated with the superoxide scavenger superoxide dismutase, further studies were conducted using a DTNB assay of the terminal sulfhydryl group of Captopril, in the presence of a biochemical generator of superoxide (hypoxanthine/xanthine oxidase). We were unable to demonstrate disappearance of the thiol group in this system, suggesting that reaction of the SH group with 02- is unlikely under our conditions. We conclude that Captopril may interfere with human PMN NADPH oxidase in vitro.
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PMID:Captopril--a potential free radical scavenger: inhibition of PMN NADPH oxidase. 284 20

Superoxide dismutase in human erythrocytes was assayed by the inhibition of highly diluted erythrocyte lysates on 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazol[1,2-alpha]pyra zin-3-one- dependent luminescence induced by the hypoxanthine-xanthine oxidase system. Our chemiluminescence procedure gave 95-times higher sensitivity than the cytochrome c method. The concentration of superoxide dismutase in erythrocytes of Down's syndrome patients was approx. 1.8-times higher than that of normal humans.
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PMID:Highly sensitive and reliable chemiluminescence method for the assay of superoxide dismutase in human erythrocytes. 284 62

Nitroaromatic compounds, which frequently contaminate the environment, are known to be reduced to corresponding aromatic amines by fish as well as mammals under anaerobic conditions. Although amine products are not generally formed aerobically, "nitroreductase"-mediated redox cycling of nitroaromatics may occur under these conditions, leading to enhanced production of a potentially toxic oxygen species, superoxide (O-2). In this study, we have investigated the ability of channel catfish (Ictalurus punctatus) hepatic microsomal and soluble fractions to stimulate O-2) production upon exposure to a model redox cycling nitroaromatic compound, nitrofurantoin (NF). Two assays for O-2 production, cytochrome c reduction and cyanide-insensitive oxygen consumption, were stimulated by NF exposure to both hepatic fractions. These reactions were partially inhibited by superoxide dismutase (SOD), and by SOD and catalase in the oxygen consumption assay, providing specific evidence for the involvement of O-2 in the stimulatory effect by NF. Furthermore, results of cofactor requirement and inhibition studies suggest that NF enhancement of O-2 production was mediated by NADPH-cytochrome P-450 (c) reductase in the microsomal fraction and xanthine oxidase in the soluble fraction. These findings comprehensively suggest that the in vitro stimulation of O-2 production by nitroaromatics as indicated in mammals may also occur in fish and, therefore, suggests a similar potential for oxyradical-mediated toxicities in these species.
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PMID:Nitrofurantoin-stimulated superoxide production by channel catfish (Ictalurus punctatus) hepatic microsomal and soluble fractions. 284 61


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