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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)

Detergent solubilized bovine milk fat globule membrane material studied by crossed immunoelectrophoresis combined with histochemical techniques revealed four major protein complexes. All four were found to bind to concanavalin A and three were identified as sialoglycoproteins. Xanthine oxidase activity was associated with the non-sialoglycoprotein precipitate. Immunoabsorption with intact milk fat globules showed an internal location of the xanthine oxidase, whereas the three other main proteins plus Mg2+-ATPase and 5'-nucleotidase were disposed on the outer membrane surface. The major proteins from milk fat globule membrane and membrane material isolated from skim milk showed immunochemical identity.
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PMID:Crossed immunoelectrophoresis of bovine milk fat globule membrane protein solubilized with non-ionic detergent. 13 25

Electrophoretic patterns of polypeptides of milk fat globule differed quantitatively depending on extent of washing during membrane preparation. This was due to selective loss of loosely associated, extrinsic membrane proteins. Major polypeptides with apparent molecular weights of 155,000 and 43,500 and membrane glycoproteins were released selectively during preparation of milk fat globule membranes. Evidence suggested that xanthine oxidase was a constituent of the selectively removed polypeptide fraction of apparent molecular weight 155,000. A major class of polypeptide with an apparent molecular weight of 62,500 was not extracted from milk fat globule membrane by treatment with dilute salts, ethylenediaminetetraacetic acid, or by nonionic and ionic detergent solutions. Milk fat globule membranes were separated into seven subfractions on isopycnic centrifugation in sucrose density gradients. Specific activities of the enzymes 5'-nucleotidase, xanthine oxidase, acid and alkaline phosphatases were similar or identical in all fractions. Electrophoretic analysis showed these seven subfractions had similar polypeptide profiles. Both phospholipid and total lipid content of subfractions were correlated inversely with fraction density. The results show that milk fat globule membrane is nearly homogenous in content of intrinsic membrane proteins and certain membrane-bound enzyme activities but is markedly heterogeneous with respect to buoyant density and lipid content.
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PMID:Membranes of mammary gland. XII. Loosely associated proteins and compositional heterogeneity of bovine milk fat globule membrane. 84 88

Adenosine produced from 5'-AMP has been proposed as a mediator of intrinsic renal regulation. The rates of 5'-AMP and adenosine metabolism are dependent on the activities of enzyme involved in purine metabolism. The activities of adenosine kinase (AK), adenosine deaminase (ADA), 5'-nucleotidase (5'-NT), AMP deaminase, xanthine oxidase and purine nucleoside phosphorylase were measured in cytosolic and membrane fractions from glomeruli, cortical tubules, medullary thick ascending limb of Henle (MTAL) and collecting duct prepared from rat kidney by combinations of sieving and sucrose density gradient centrifugation techniques. In the cytoplasm of glomeruli cells, the activity ratios of ADA/AK and AMP deaminase/5'-NT were 70 and 2.4, respectively. The highest activity of 5'-NT was found in membrane fractions of cortical tubules where it was equally distributed between luminal and antiluminal membranes. Membrane fractions of MTAL did not contain detectable amounts of adenosine deaminase activity. The highest activity of xanthine oxidase and purine nucleoside phosphorylase was in the cytoplasm fraction of glomeruli. These results suggest that deamination of AMP and adenosine may be favored in the cytoplasm of glomeruli cells. In contrast, in the extracellular space of glomeruli and especially in the cortical tubule, AMP can be converted preferentially to adenosine by 5'-NT.
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PMID:The distribution of enzymes involved in purine metabolism in rat kidney. 161 Aug 88

Uptake and release of purines by red blood cells has been shown to be markedly sensitive to changes in pH, inorganic phosphate (Pi), and oxygen concentration (Berman, P., Black, D., Human, L., and Harley, E. (1988) J. Clin. Invest. 82, 980-986). The mechanism of this regulation has been further studied. We have shown that incubation of red cells in medium containing xanthine oxidase rapidly and completely depletes intracellular hypoxanthine and causes accumulation of 5-phosphoribosyl 1-pyrophosphate (PRPP) at physiological Pi concentrations. Hypoxanthine release from intracellular IMP is strictly dependent on PRPP depletion, induced by either alkalinizing the cells or by adding excess adenine. Xanthine oxidase abolishes this dependence. Oxygen depletion enhances adenine uptake and prevents hypoxanthine release. The results suggest that hypoxanthine release is governed by PRPP-dependent recycling of hypoxanthine to IMP. We propose that PRPP accumulation in red cells is regulated by a substrate cycle, comprising hypoxanthine, IMP, and inosine. Cycle flux is controlled by Pi inhibition and 2,3-bisphosphoglycerate activation of purine-5'-nucleotidase, which converts IMP to inosine. Oxypurine cycling may account for the sensitive control of purine uptake and release by changes in pH and oxygen tension that occur physiologically.
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PMID:Regulation of 5-phosphoribosyl 1-pyrophosphate and of hypoxanthine uptake and release in human erythrocytes by oxypurine cycling. 169 Nov 71

The effect of repeated administration of allopurinol (50 mg.kg-1 48, 24, and 4 hours before analysis) on the activity of enzymes of degradation and resynthesis of adenine nucleotides was studied. The activity of xanthine dehydrogenase and xanthine oxidase was inhibited in the heart, liver and kidney and the activity of membrane-bound 5'-nucleotidase was particularly elevated in the heart and brain, suggesting that membrane transport processes may be affected. The increase in the activity of hypoxanthine guanine phosphoribosyl transferase in the liver is indicative of a potential mechanism of positive action of allopurinol upon restoring the purine nucleotide store. The authors present their hypothesis on the mechanism of allopurinol action upon the metabolism of adenine nucleotides. The suggested mechanisms might become operative in protecting tissues against ischemia and reperfusion induced damage.
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PMID:[Mechanisms of the effect of allopurinol on the metabolism of adenine nucleotides]. 191 98

1. Adenosine metabolizing enzymes in seminal plasma of man and bull have been investigated. 2. A different level of 5'-nucleotidase activity has been found in two seminal plasmas: in bull 5'-nucleotidase represents 80% of the total AMP dephosphorylating enzymes while in man 5'-nucleotidase represents only 1.3% of the total AMP dephosphorylating activities. 3. Apart from the different levels of 5'-nucleotidase activity, different kinetic parameters have been reported for 5'-nucleotidase, acid prostatic phosphatases, ADA and PNP. 4. Adenosine kinase, xanthine oxidase and AdoHcy-hydrolase have not been detected in the seminal plasma of man and bull.
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PMID:Adenosine metabolizing enzymes in seminal plasma of bull and man: a comparative study. 212 26

Acetylcholine and ATP are costored and coreleased during synaptic activity at the electric organ of Torpedo. It has been suggested that released ATP is converted to adenosine at the synaptic cleft, and in turn this nucleoside would depress the evoked release of acetylcholine. In the present communication we have used a chemiluminescent reaction that let us to monitor continuously the presence of adenosine in this preparation. The chemiluminescent reaction is based on the conversion of adenosine into uric acid and H2O2 by adenosine deaminase, nucleoside phosphorylase, and xanthine oxidase enzymes. The hydrogen peroxide has been detected by peroxidase-luminol mixture. The reaction has a sensitivity on the picomol range and discerned between Adenosine, AMP, ADP, and ATP. We have developed this technique in the hope of understanding whether adenosine is released during synaptic activity or it comes from the released ATP. We have studied the release or formation of adenosine in fragments of the electric organ and in isolated cholinergic nerve terminals obtained from it. In both conditions we have followed the effect of potassium stimulation upon the detection of adenosine. Potassium stimulation increased the extracellular adenosine either in slices or the synaptosomal fraction of Torpedo electric organ. The presence of alpha, beta-methylene ADP, an inhibitor of 5'-nucleotidase, inhibits the detection of adenosine, suggesting that extracellular adenosine is a consequence of ectocellular dephosphorylation of released ATP.
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PMID:The release of adenosine at the electric organ of Torpedo. A study using a continuous chemiluminescent method. 232 27

The present study was undertaken to determine whether significant breakdown of adenine nucleotides to purine bases and oxypurines occurred in mitochondria following myocardial ischemia and ischemia followed by reperfusion, and whether allopurinol prevented this effect. The adenine nucleotides adenosine, hypoxanthine, xanthine and uric acid were measured in the mitochondria and the results suggest that breakdown did occur. Malondialdehyde concentration was determined to gauge lipid peroxidation. This substance did not increase during ischemia or reperfusion, but did so in the presence of allopurinol. Xanthine dehydrogenase was converted to xanthine oxidase during reperfusion and the activity of both enzymes were inhibited by allopurinol. The results also suggested the presence of a mitochondrial 5'-nucleotidase. We conclude that significant breakdown of adenine nucleotide took place in myocardial mitochondria during ischemia and ischemia followed by reperfusion and that allopurinol may have a protective effect.
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PMID:Purine and oxypurine production in mitochondria of ischemic and reperfused myocardium. 261 53

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.
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PMID:An enzymatic inosine 5'-monophosphate assay of increased specificity. 298 81

Coupled enzyme assays are described for measuring inorganic phosphates, organic phosphates and phosphate-liberating enzymes in biological material. The assays all determine Pi by its reaction with inosine, catalysed by nucleoside phosphorylase; this yields ribose 1-phosphate and hypoxanthine. The hypoxanthine is oxidized to uric acid by xanthine oxidase, and may be measured either by the absorbance of the uric acid, or by the formazan formed when a tetrazolium salt is used as the oxidant. The coupled enzyme assays are characterized by high sensitivity, quantitative utilization of phosphates and stoichiometric formation of the measurable products, measurement at pH 6.0-8.5, determination of phosphates within a single analytical step, and continuous measurement of phosphohydrolase activity in a corresponding rate assay. Examples include determinations of substrates such as Pi, PPi and AMP, and of enzymes such as 5'-nucleotidase, inorganic pyrophosphatase and glucose-6-phosphatase. Directions for further examples are given.
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PMID:Enzymic determination of inorganic phosphates, organic phosphates and phosphate-liberating enzymes by use of nucleoside phosphorylase-xanthine oxidase (dehydrogenase)-coupled reactions. 299 93


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