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

---

Query: EC:1.17.3.2 (xanthine oxidase)
8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The enzymatic inosine 5'-monophosphate assay described by Grassl [in, Methods of Enzymatic Analysis (H. U. Bergman, ed.), pp. 2168-2171, Academic Press, New York (1974)] is highly nonspecific, as ITP, ATP, ADP, AMP, and adenosine react stoichiometrically. The reactivity with the adenine derivatives is due to the tri- and diphosphatase activity of alkaline phosphatase (AP), coupled with adenosine deaminase (and possibly AMP deaminase) contamination of commercially available preparations of AP, purine-nucleoside phosphorylase, and/or xanthine oxidase. The inclusion of coformycin (0.05 microgram/ml), a potent inhibitor of these deaminases, completely eliminated the cross-reactivity. ITP, however, still reacted stoichiometrically due to the tri- and diphosphatase activity of AP. Meyer and Terjung [Amer. J. Physiol. 237 C111-C118 (1979)] introduced a modification of Grassl's procedure, substituting 5'-nucleotidase for AP. It has been found that this disallows reactivity with ATP, ADP, and ITP but that AMP and adenosine still react completely. Coformycin prevents this cross-reactivity. It is therefore recommended that the assay be carried out with 5'-nucleotidase (instead of AP) and coformycin, in order to achieve a more specific assay, and one more suitable for use with whole tissue extracts.
...
PMID:An enzymatic inosine 5'-monophosphate assay of increased specificity. 298 81

The superoxide radicals generated by the xanthine oxidase reaction reduced the myofibrillar Ca2+-ATPase activity. This negative effect was prevented by superoxide dismutase or by dithiothreitol, a protective thiol compound. Partial protection was achieved by catalase, while mannitol was ineffective. The myofibrillar Ca2+-ATPase exposed to O2-. radicals did not modify the affinity for Ca2+ while it showed a remarkable reduction of Vmax measured at the saturating level of Ca2+. The O2-. inhibited myofibrillar ATPase showed a higher value of Km for the cofactor associated to a reduced value of Vmax when studied in the presence of increasing concentration of ATP. Thus, circumstances that enhance the production of cardiac O2- radicals can be considered a negative metabolic event capable of depressing the myofibrillar Ca2+-ATPase activity.
...
PMID:Inhibitory effect of superoxide radicals on cardiac myofibrillar ATPase activity. 299 80

O2- was produced by gamma irradiation of formate solutions, by the action of xanthine oxidase on hypoxanthine and O2, and by the action of ferredoxin reductase on NADPH and paraquat in the presence of O2. Its reaction with H2O2 and various iron chelates was studied. Oxidation of deoxyribose to thiobarbituric acid-reactive products that was appropriately inhibited by OH. scavengers, or formate oxidation to CO2, was used to detect OH(.). With each source of O2-, and by these criteria, Fe(EDTA) efficiently catalyzed this (Haber-Weiss) reaction, but little catalysis was detectable with iron bound to DTPA, citrate, ADP, ATP, or pyrophosphate, or without chelator in phosphate buffer. O2- produced from xanthine oxidase, but not from the other sources, underwent another iron-dependent reaction with H2O2, to produce an oxidant that did not behave as free OH(.). It was formed in phosphate or bicarbonate buffer, and caused deoxyribose oxidation that was readily inhibited by mannitol or Tris, but not by benzoate, formate, or dimethyl sulfoxide. It did not oxidize formate to CO2. Addition of EDTA changed the pattern of inhibition to that expected for a reaction of OH(.). The other chelators all inhibited deoxyribose oxidation, provided their concentrations were high enough. The results are compatible with iron bound to xanthine oxidase catalyzing production of a strong oxidant (which is not free OH.) from H2O2 and O2- produced by the enzyme.
...
PMID:Iron and xanthine oxidase catalyze formation of an oxidant species distinguishable from OH.: comparison with the Haber-Weiss reaction. 300 38

The effects of allopurinol pretreatment (1 mg/ml in the drinking water for 7 days at an estimated daily dose of 75 mg/kg) on biochemical and chemical changes occurring following left circumflex coronary artery ligation (40 min) and reperfusion (60 min) were examined in pentobarbital-anesthetized rabbits. During the ischemic phase, allopurinol pretreatment provided significant preservation of cellular ATP levels and of mitochondrial ATP generation as compared with untreated animals (P less than 0.05). During the reperfusion phase, allopurinol pretreatment significantly prevented the decrease in left ventricular pressure, sodium and calcium accumulation and decreases in sarcolemmal Na+,K+-stimulated and sarcoplasmic reticulum K+,Ca2+-stimulated ATPase activities as compared with untreated animals (P less than 0.05). In contrast, the decrease in mitochondrial (azide-sensitive) ATPase during ischemia and the partial recovery during reperfusion were unaffected by allopurinol pretreatment. Our results indicate that the myocardial protective effects of allopurinol may differ mechanistically in the ischemic and reperfusion phases of injury. The fact that rabbit hearts do not contain detectable xanthine oxidase activity would seem to preclude an obligatory role of this enzyme both in the generation of myocardial ischemic/reperfusion injury and in the protective actions of allopurinol.
...
PMID:Effects of allopurinol on myocardial ischemic injury induced by coronary artery ligation and reperfusion. 303 15

In this lecture, evidence is presented to support the following hypothesis regarding the roles of xanthine oxidase-derived oxidants and granulocytes in ischemia-reperfusion-induced microvascular injury. During the ischemic period, ATP is catabolized to yield hypoxanthine. The hypoxic stress also triggers the conversion of NAD-reducing xanthine dehydrogenase to the oxygen radical-producing xanthine oxidase. During reperfusion, molecular oxygen is reintroduced into the tissue where it reacts with hypoxanthine and xanthine oxidase to produce a burst of superoxide anion and hydrogen peroxide. In the presence of iron, superoxide anion and hydrogen peroxide react via the Haber-Weiss reaction to form hydroxyl radicals. This highly reactive and cytotoxic radical then initiates lipid peroxidation of cell membrane components and the subsequent release of substances that attract, activate, and promote the adherence of granulocytes to microvascular endothelium. The adherent granulocytes then cause further endothelial cell injury via the release of superoxide and various proteases.
...
PMID:Role of xanthine oxidase and granulocytes in ischemia-reperfusion injury. 305 26

The role of free radicals in the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by a membrane-bound enzyme from carnation petals was studied. The membrane preparation oxidized ACC more effectively than it oxidized cyclopropaneamine or 2-keto-4-methylthiobutyric acid (KMB). All these substrates were oxidized chemically by NaOCl to ethylene very effectively. Free radicals generated by the xanthine/xanthine oxidase system oxidized KMB far more effectively than it oxidized ACC; only 0.004% of the ACC included in the reaction mixture was oxidized in 1 h, compared with 0.9% of the KMB. Conversion of ACC to ethylene by the membrane-bound enzyme was inhibited by Co2+, ATP and EDTA, while the inhibition of the oxidation of KMB by the same inhibitors was much less pronounced. These results suggest that ACC, the natural immediate precursor of ethylene, is specifically oxidized by the membrane-bound enzyme rather than through a nonspecific oxidation by free radicals.
...
PMID:Free radicals play little role in the conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene in carnation membrane fraction. 314 43

Age-dependent differences in the effects of ischemia and reperfusion on ATP breakdown were studied in perfused adult and newborn (10 days old) rat hearts. No-flow ischemia (15 min at 37, 30, or 23 degrees C) was applied and reperfusion (20 min at 37 degrees C) was studied after ischemia at 23 or 37 degrees C. Hypothermia during ischemia protected both age groups to a similar degree against ATP decline, which was linear with temperature. Reperfusion after normothermic ischemia resulted in higher ATP levels in newborn hearts with less release of ATP catabolites (purines). We found no age-related differences in lactate release but large differences in purine release. During normoxia, adult hearts released mainly urate (80% of total) and inosine (7%), but newborns released hypoxanthine (64%) and inosine (15%). Early during reperfusion adult hearts released inosine (58%) and adenosine (18%), but newborns released inosine (53%) and hypoxanthine (38%). These data suggested a lower activity of the potentially deleterious enzyme xanthine oxidoreductase in newborn hearts, which was confirmed by enzymatic assay. ATP-catabolite release during reperfusion was less in newborn than adult hearts, and this coincided with lower xanthine oxidase activity.
...
PMID:Different ATP-catabolism in reperfused adult and newborn rat hearts. 316 69

Xanthine oxidase increases the rate of actin polymerization. This occurs at oxidase concentrations as low as 40 nM provided the concentration of the polymerizing agent is low (0.5 mM MgCl2). In the presence of 0.1 M KCl plus 1 mM MgCl2 as the polymerizing agents, xanthine oxidase does not affect the rate of the polymerization but increases significantly the rate of the conversion of F(ATP)actin into F(ADP.Pi)actin and probably also the rate of the orthophosphate release.
...
PMID:On the interaction between xanthine oxidase and actin. 319 Jul 22

When incubated with mitochondria in an air atmosphere, menadione and doxorubicin (which redox cycle with the respiratory chain to produce oxygen radicals), as well as xanthine oxidase plus xanthine (which generate superoxide and H2O2), stimulated the degradation of newly-synthesized [( 3H]leucine-labelled) mitochondrial polypeptides. No stimulation was observed in an N2 atmosphere, ATP was not required, and xanthine oxidase was not effective without xanthine. Various forms of oxidative stress induced varying degrees of protein cross-linking, protein fragmentation and proteolysis, as judged by gel electrophoresis and amino acid analysis. To learn more about the proteolytic enzymes involved in degradation, we undertook studies with purified protein substrates which had been exposed to oxidative stress (OH or H2O2) in vitro. Despite mitochondrial contamination with acid proteases of lysosomal (and other) origin, pH profiles revealed distinct proteolytic activities at both pH 4 and pH 8. The pH 8 activity preferentially degraded the oxidatively-denatured forms of haemoglobin, albumin and superoxide dismutase; was unaffected by digitonin; and exhibited a several-fold increase in activity upon mitochondrial disruption (highest activity being found in the matrix). In contrast, the pH 4 activity was dramatically decreased by digitonin treatment (to reduce lysosomal contamination); was unaffected by mitochondrial disruption; and showed no preference for oxidatively-denatured proteins. The pH 8 activity was not stimulated by ATP, but was inhibited by EDTA, haemin and phenylmethylsulphonyl fluoride. In contrast, the contaminating pH 4 activity was only inhibited by pepstatin and leupeptin. Thus, our experiments reveal a distinct mitochondrial (matrix) proteolytic pathway which can preferentially degrade oxidatively-denatured proteins.
...
PMID:Mitochondria contain a proteolytic system which can recognize and degrade oxidatively-denatured proteins. 319 85

Based on work from our laboratory and studies by others, we propose the following hypothesis to explain the interaction among xanthine oxidase, PMNs, and tissue injury in the postischemic small intestine (Figure 2). During the ischemic period, ATP is catabolized to yield hypoxanthine. The hypoxic stress also triggers the conversion of NAD-reducing xanthine dehydrogenase to the oxygen radical-producing xanthine oxidase via a protease. When the intestine is reperfused, molecular oxygen is reintroduced into the tissue where it reacts with hypoxanthine and xanthine oxidase to produce a burst of superoxide anion and hydrogen peroxide. In the presence of ferric iron, superoxide anion and hydrogen peroxide react via the Haber-Weiss reaction to form hydroxyl radicals. This highly reactive and cytoxic free radical then initiates lipid peroxidation of cell membrane components and the subsequent release of substances that activate, attract, and promote the adherence of PMN to microvascular endothelium. The adherent PMN then causes further endothelial cell injury via the release of superoxide and various proteases.
...
PMID:Mechanisms of oxidant-mediated microvascular injury following reperfusion of the ischemic intestine. 325 May 38


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---