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At least 19 recordsLinked to original sources
PubMed1996

[The role of xanthine dehydrogenase (xanthine oxidase) in ischemia-reperfusion injury in rat kidney].

Xanthine dehydrogenase (XDH) and xanthine oxidase (XO) are enzymes involved in the metabolism of purines in various organisms. XO produces superoxide radicals, suggesting that is responsible for tissue ischemia-reperfusion injury. To test this notion further studies were performed on rat kidneys and the time course of changes in purine nucleotides, oxypurines and XDH and XO activity was determined. At 24 hours after reperfusion subsequent to 30-minute ischemia, serum creatinine increased to 0.83 +/- 0.74 mg/dl from 0.28 +/- 0.06 mg/dl (the level prior to ischemia, the control). Renal ATP and ADP contents were reduced after ischemia lasting for 30 minutes and restored 10 minutes after reperfusion following 30 minutes of ischemia. The renal AMP content increased after 30 minutes of ischemia and recovered within 10 minutes after reperfusion. The total adenine nucleotide (TAN) content was reduced gradually during ischemia-reperfusion in the rat kidney. Although the energy charge was reduced following 30 minutes of ischemia, it was restored to the control level 10 minutes following reperfusion. Hypoxanthine (HX) and xanthine (X), which had accumulated at 30 minutes after ischemia, were reduced to the control levels 10 minutes after reperfusion. There were no significant changes in the pre-ischemia values of total XDH and XO activities or XDH/XO ratio during the period nor at various time intervals (up to 24 hours) during reperfusion. It was shown that HX and X accumulate without significant conversion of XDH to XO during ischemia. Therefore the putative role of XO in ischemia-reperfusion injury seems to more complex than initially predicted.

Animals↗
PubMed1977

Comparative activity and properties of lactate dehydrogenase, xanthine dehydrogenase, and dihydrofolate reductase in normal and Brugia pagangi-infected Aedes aegypti.

The amount of xanthine dehydrogenase (XDH), dihydrofolate reductase (DHFR), and lactate dehydrogenase (LDH) in crude extracts of 4- to 5-day-old adult Aedes aegypti was determined, and the properties of these enzymes were partially characterized. It was then found that the amount and other selected characteristics of XDH and LDH in extracts of female Ae. aegypti processed 5 to 7 days and 12 to 14 days after they had fed upon either normal or Brugia pahangi-infected jirds were indistinguishable from those of these two enzymes in extracts of female mosquitoes that did not have a blood meal. Under the same circumstances, the selected characteristics of DHFR were also unaffected. However, there was a suggestion that the amount of DHFR was slightly increased in extracts of female Ae. aegypti processed 5 to 7 days after they had fed upon B. pahangi-infected jirds; by 12 to 14 days after the blood meal, there was a consistent 30% to 60% increase in the amount of DHFR inextracts of infected mosquitoes. DHFR activity could not be detected in a similarly prepared extract of 4,000 to 5,000 infective (L-3) B. pagangi larvae, the approximate number present in the infected mosquito extracts. It would appear, therefore, that the increased amount of turnover of DHFR in the mosquito host occurs in response to advanced infection with B. pahangi.

Aedes↗
PubMed1994

Regulation of endothelial cell xanthine dehydrogenase xanthine oxidase gene expression by oxygen tension.

Recent studies have demonstrated that xanthine dehydrogenase/xanthine oxidase (XD/XO) activities of bovine endothelial cells (EC) are inversely regulated by O2 tensions to which the cells are exposed. We have confirmed these reports and extended the observation to a variety of cells from other sources. All EC that had detectable XD/XO activity demonstrated the greatest activity at the lowest O2 level. Bovine pulmonary artery smooth muscle cells showed XD/XO activity only under hypoxic conditions. The ratio of XO to XO+XD did not change significantly under various O2 concentrations for all cell types tested. Treatment of bovine pulmonary artery and rat epididymal fat pad EC with actinomycin D (1 microgram/ml), an inhibitor of transcription, suppressed XO and XO+XD activities in cells exposed both to 20 and 3% O2. High-dose cycloheximide (5 micrograms/ml), an inhibitor of translation, also reduced XO and XO+XD activities in these cells, whereas low-dose cycloheximide (0.5 microgram/ml) enhanced the stimulatory effect of hypoxia on XO+XD activity. We developed a digoxigenin-labeled probe that recognizes and hybridizes to rat XD cDNA and used it to examine the effect of O2 concentration on XD/XO mRNA expression of rat epididymal fat pad EC. XD/XO mRNA concentration was increased in cells exposed to hypoxia and decreased in cells exposed to hyperoxia compared with normoxic cells. The increase in mRNA concentration resulting from exposure to hypoxia was enhanced by cycloheximide. There was no change in XD/XO mRNA stability in cells exposed to hypoxia compared with normoxia. We conclude that the regulation of XD/XO by oxygen tension most likely occurs at the transcriptional level.

Adipose Tissue↗
PubMed2005

Mechanism of the conversion of xanthine dehydrogenase to xanthine oxidase: identification of the two cysteine disulfide bonds and crystal structure of a non-convertible rat liver xanthine dehydrogenase mutant.

Mammalian xanthine dehydrogenase can be converted to xanthine oxidase by modification of cysteine residues or by proteolysis of the enzyme polypeptide chain. Here we present evidence that the Cys(535) and Cys(992) residues of rat liver enzyme are indeed involved in the rapid conversion from the dehydrogenase to the oxidase. The purified mutants C535A and/or C992R were significantly resistant to conversion by incubation with 4,4'-dithiodipyridine, whereas the recombinant wild-type enzyme converted readily to the oxidase type, indicating that these residues are responsible for the rapid conversion. The C535A/C992R mutant, however, converted very slowly during prolonged incubation with 4,4'-dithiodipyridine, and this slow conversion was blocked by the addition of NADH, suggesting that another cysteine couple located near the NAD(+) binding site is responsible for the slower conversion. On the other hand, the C535A/C992R/C1316S and C535A/C992R/C1324S mutants were completely resistant to conversion, even on prolonged incubation with 4,4'-dithiodipyridine, indicating that Cys(1316) and Cys(1324) are responsible for the slow conversion. The crystal structure of the C535A/C992R/C1324S mutant was determined in its demolybdo form, confirming its dehydrogenase conformation.

Animals↗
PubMed1979

Kinetics and stability of immobilized chicken liver xanthine dehydrogenase.

Xanthine dehydrogenase (EC 1.2.1.37) was isolated from chicken livers and immobilized by adsorption to a Sepharose derivative, prepared by reaction of n-octylamine with CNBr-activated Sepharose 4B. Using a crude preparation of enzyme for immobilization it was observed that relatively more activity was adsorbed than protein, but the yield of immobilized activity increased as a purer enzyme preparation was used. As more activity and protein were bound, relatively less immobilized activity was recovered. This effect was probably due to blocking of active xanthine dehydrogenase by protein impurities. The kinetics of free and immobilized xanthine dehydrogenase were studied in the pH range 7.5-9.1. The Km and V values estimated for free xanthine dehydrogenase increase as the pH increase; the K'm and V values for the immobilized enzyme go through a minimum at pH 8.1. By varying the amount of enzyme activity bound per unit volume of gel, it was shown that K'm is larger than Km are result of substrate diffusion limitation in the pores of the support material. Both free and immobilized xanthine dehydrogenase showed substrate activation at low concentrations (up to 2 microM xanthine). Immobilized xanthine dehydrogenase was more stable than the free enzyme during storage in the temperature range of 4-50 degrees C. The operational stability of immobilized xanthine dehydrogenase at 30 degrees C was two orders of magnitude smaller than the storage stability, t 1/2 was 9 and 800 hr, respectively. The operational stability was, however, better than than of immobilized milk xanthine oxidase (t 1/2 = 1 hr). In addition, the amount of product formed per unit initial activity in one half-life, was higher for immobilized xanthine dehydrogenase than for immobilized xanthine oxidase. Unless immobilized milk xanthine oxidase can be considerable stabilized, immobilized chicken liver xanthine dehydrogenase is more promising for application in organic synthesis.

Animals↗
PubMed1992

Change of xanthine dehydrogenase and xanthine oxidase activities in rat brain following complete ischaemia.

We studied the activities of xanthine dehydrogenase and xanthine oxidase in rat forebrain after complete ischaemia. Complete ischaemia was induced by decapitation after transcardiac infusion with saline. The activities of xanthine dehydrogenase and xanthine oxidase immediately after ischaemia were 93.3 +/- 38.7 and 18.8 +/- 7.7 microU/mg protein, respectively, and at 24 h after ischaemia were 183.5 +/- 75.1 and 60.8 +/- 15.2 microU/mg protein, respectively. The ratios of xanthine dehydrogenase/xanthine oxidase immediately and 24 h after ischaemia were 5.04 +/- 1.03 and 3.04 +/- 0.99, respectively. These data indicate that xanthine dehydrogenase and xanthine oxidase activities were maintained even 24 h after complete ischaemia. Conversion of xanthine dehydrogenase to xanthine oxidase proceeds slowly during complete ischaemia.

Animals↗
PubMed1994

Conversion of xanthine dehydrogenase into xanthine oxidase in rat liver and plasma at the onset of reperfusion after ischemia.

The aim of this study was to test whether conversion of xanthine dehydrogenase into xanthine oxidase as induced by fasting, ischemia of the liver or both is an in vivo process or only occurs in vitro in homogenates. For this purpose, the conversion rate of xanthine dehydrogenase into xanthine oxidase was studied in liver homogenates obtained from rats after normal feeding or 24 hr of fasting followed or not by 2 hr of ischemia of the liver. In fed rats, the conversion rate of xanthine dehydrogenase into xanthine oxidase was studied as well in liver homogenates after different periods of reperfusion after 2 hr of ischemia. Homogenization was carried out under strictly controlled conditions, after which the supernatants were incubated at 37 degrees C in buffer for 0 to 5 hr. Enzyme activities were assayed spectrophotometrically by measuring urate production at 295 nm. Conversion started only after 2 to 3 hr of incubation of supernatants of control fed livers, whereas conversion started immediately after 24 hr of fasting. The percentage oxidase activity of total xanthine oxidoreductase activity in ischemic livers from fed animals was slightly higher (26.7% +/- 1.7%; p < 0.05) than in control livers (19.3% +/- 1.4%), whereas the percent oxidase activity in ischemic livers from fasted animals (16.7% +/- 1.0%) was not different from that in control animals (16.8% +/- 1.1%). Ischemia for 2 hr caused in vitro a substantial increase in the conversion rate in supernatants of livers of fed and fasted rats as compared with their controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Mechanism of neutrophil-induced xanthine dehydrogenase to xanthine oxidase conversion in endothelial cells: evidence of a role for elastase.

Activated neutrophils cause conversion of xanthine dehydrogenase to its oxidase form (xanthine oxidase) in endothelial cells, the mechanism of which may be related to the cytotoxic effect of activated neutrophils. The elastase inhibitors, elastatinal, alpha 1-antitrypsin, and MeO-Suc-(Ala)2-Pro-Val-CH2Cl, significantly inhibited xanthine dehydrogenase to oxidase conversion by phorbol myristate acetate-stimulated neutrophils without inhibition of neutrophil adherence to the endothelial cell monolayer. The role of elastase in this enzyme conversion process was confirmed by the ability of purified elastase to cause conversion of xanthine dehydrogenase to xanthine oxidase in intact endothelial cells (or cell extracts) without causing cytotoxicity. In contrast, cathepsin G failed to cause conversion. The kinetics of conversion induced by elastase was relatively rapid, being essentially completed by 30 min. Upon removal of elastase, the effect was slowly (greater than 12 h) reversible and could be inhibited by cycloheximide treatment. Exposure of endothelial cells to hypoxia failed to enhance the elastase-induced conversion. Treatment of endothelial cells with Ca2+ ionophores failed to cause conversion of xanthine dehydrogenase to oxidase, suggesting that intracellular Ca(2+)-activated proteases are not sufficient to induce this process. Neutrophil-induced xanthine dehydrogenase to oxidase conversion was inhibited by concomitant treatment with antibodies to CD11b. The results suggest that activated neutrophils induce conversion of xanthine dehydrogenase to oxidase by secretion of elastase in close proximity to the endothelial cells and that this intimate contact between the two cell types enables high local concentrations of elastase to be attained, which are sufficient to cause xanthine dehydrogenase to xanthine oxidase conversion.

Animals↗
PubMed1988

Reoxygenation injury in isolated hepatocytes: cell death precedes conversion of xanthine dehydrogenase to xanthine oxidase.

Reoxygenation of isolated hepatocytes from fed rats after 3 h of anaerobic incubation led to a significantly enhanced loss of cell viability. No evidence for the participation of reactive oxygen species generated by xanthine oxidase in this reoxygenation injury was found. Conversion of xanthine dehydrogenase to xanthine oxidase occurred at a time when almost all of the hepatocytes had lost their viability. Furthermore, xanthine dehydrogenase was first released from the severely injured cells and then converted to the oxidase form. The results suggest that in the intact organ participation of reactive oxygen species, generated by xanthine oxidase, in reoxygenation injury may only occur when, upon reoxygenation, hypoxic cell injury in part of the tissue has progressed to such an extent that there is a significant conversion of xanthine dehydrogenase to xanthine oxidase.

Anaerobiosis↗
PubMed1996

[Xanthine oxidase (xanthine dehydrogenase)].

Xanthine oxidase (xanthine dehydrogenase) is composed of two identical subunits of approximately 150,000 daltons. Each subunit contains four oxdation-reduction active cofactors/monomers. In vivo, the enzyme exists mostly as the dehydrogenase type (the NAD-dependent type). The cDNA has been cloned from human liver, and the amino acid sequence has been determined. As xanthine oxidase seems to produce superoxide in postischemic reperfusion, the relation between the superoxide and postischemic tissue injury has been discussed. It has also been reported that inhibition of xanthine oxidase by allopurinol may cause severe 6-mercaptopurine toxicity.

DNA↗
PubMed1989

Proteolytic conversion of xanthine dehydrogenase to xanthine oxidase: evidence against a role for calcium-activated protease (calpain).

The present study tested the hypothesis that calpain is responsible for the limited proteolytic conversion of xanthine dehydrogenase (XD) to xanthine oxidase (XO). We compared the effects of various proteases on the activity and molecular weight of a purified preparation of xanthine dehydrogenase from rat liver. In agreement with previous reports, trypsin treatment produced a complete conversion of XD to XO accompanied by a limited proteolysis of XDH from an Mr of 140 kD to an Mr of 90 kD. Treatment with calpain I or calpain II did not produce a conversion from XD to XO nor did it result in partial proteolysis of the enzyme. Similarly, trypsin treatment partially degraded a reversibly oxidized form of xanthine dehydrogenase while calpain I or calpain II were ineffective. The possibility that an endogenous inhibitor prevented the proteolysis of XDH by calpain I or II was excluded by verifying that brain spectrin, a known calpain substrate, was degraded under the same incubation conditions. The results indicate that calpain is not likely to be responsible for the in vivo conversion of XD to XO under pathological conditions.

Animals↗
PubMed1995

Flavoprotein structure and mechanism. 4. Xanthine oxidase and xanthine dehydrogenase.

Xanthine oxidase and xanthine dehydrogenase are enzymes involved in the metabolism of purines and pyrimidines in various organisms. Their relationship to one another has been the subject of considerable debate, primarily because of their proposed roles in ischemia/reperfusion damage in tissues. Differences in the kinetics and oxidation-reduction behavior of the two forms are accounted for by the presence in the dehydrogenase of a binding site for NAD+, as well as a substantially lower reduction potential for the flavin FADH./FADH2 couple of the dehydrogenase relative to the oxidase. This review presents recent advances of our understanding of the biochemistry and molecular biology of these systems, including a model for the overall morphology of xanthine oxidizing enzymes. The evidence that the two enzymes represent alternate forms of the same gene product, in some cases reversibly interconvertible between one another, is discussed.

Animals↗
PubMed2003

Protein film voltammetry of Rhodobacter capsulatus xanthine dehydrogenase.

Xanthine dehydrogenase (XDH) from the bacterium Rhodobacter capsulatus catalyzes the hydroxylation of xanthine to uric acid with NAD(+) as the electron acceptor. R. capsulatus XDH forms an (alphabeta)(2) heterotetramer and is highly homologous to homodimeric eukaryotic XDHs. The crystal structures of bovine XDH and R. capsulatus XDH showed that the two proteins have highly similar folds; however, R.capsulatus XDH is at least 5 times more active than bovine XDH and, unlike mammalian XDH, does not undergo the conversion to the oxidase form. Here we demonstrate electrocatalytic activity of the recombinant enzyme, expressed in Escherichia coli, while immobilized on an edge plane pyrolytic graphite working electrode. Furthermore, we have determined all redox potentials of the four cofactors (Mo(VI/V), Mo(V/IV), FAD/FADH, FADH/FADH(2) and two distinct [2Fe-2S](2+/+) clusters) using a combination of potentiometric and voltammetric methods. A novel feature identified in catalytic voltammetry of XDH concerns the potential for the onset of catalysis (ca. 400 mV), which is at least 600 mV more positive than that of the highest potential cofactor. This unusual observation is explained on the basis of a pterin-associated oxidative switch during voltammetry that precedes catalysis.

Catalysis↗
PubMed2004

The role of active site glutamate residues in catalysis of Rhodobacter capsulatus xanthine dehydrogenase.

Xanthine dehydrogenase (XDH) from the bacterium Rhodobacter capsulatus catalyzes the hydroxylation of xanthine to uric acid with NAD+ as the electron acceptor. R. capsulatus XDH forms an (alphabeta)2 heterotetramer and is highly homologous to homodimeric eukaryotic xanthine oxidoreductases. Here we first describe reductive titration and steady state kinetics on recombinant wild-type R. capsulatus XDH purified from Escherichia coli, and we then proceed to evaluate the catalytic importance of the active site residues Glu-232 and Glu-730. The steady state and rapid reaction kinetics of an E232A variant exhibited a significant decrease in both kcat and kred as well as increased Km and Kd values as compared with the wild-type protein. No activity was determined for the E730A, E730Q, E730R, and E730D variants in either the steady state or rapid reaction experiments, indicating at least a 10(7) decrease in catalytic effectiveness for this variant. This result is fully consistent with the proposed role of this residue as an active site base that initiates catalysis.

Binding Sites↗
PubMed1991

Influence of disodium aurothiomalate on the activities of xanthine dehydrogenase and xanthine oxidase in endothelial cells.

The effect of aurothiomalate in modulating the conversion of xanthine dehydrogenase to its superoxide producing oxidase form in rat and human liver cytosolic preparations has been investigated. Low concentrations (10(-8)-10(-5) mol.dm-3) of this second-line agent were found to inhibit the conversion of the dehydrogenase to its corresponding oxidase form. High concentrations (10(-4) mol.dm-3), however, accelerated this conversion. It is possible that the influence of aurothiomalate on the relative proportions of xanthine dehydrogenase and xanthine oxidase is a reflection of the gold(I) blockage of critical thiol(ate) or sulphido ligands present in this enzymatic system. These effects may form the basis of aurothiomalate's anti-proliferative action on endothelial cells.

Animals↗
PubMed1995

Excitotoxic increase of xanthine dehydrogenase and xanthine oxidase in the rat olfactory cortex.

Excitotoxic lesions induced by systemic injection of kainic acid, resulted in 2-3-fold increase of xanthine dehydrogenase and xanthine oxidase activities in the rat olfactory cortex 48-72 h after drug administration. A significant increase of the xanthine oxidase/dehydrogenase ratio was also observed at 4 and 48 h post-injection. No similar changes were noticed in the hippocampus. The enhancement of enzyme activity seems to be primarily a consequence of the altered cell composition in damaged area. Free radicals produced by the increased oxygen-dependent form of the enzyme could in turn aggravate the excitotoxic brain injury.

Animals↗
PubMed1988

Mechanisms of conversion of xanthine dehydrogenase to xanthine oxidase in ischemic rat liver and kidney.

Previous studies have proposed and supported a role for the proteolytic, irreversible conversion of xanthine dehydrogenase to xanthine oxidase (XO) in postischemic injury in a wide variety of organs. A second mechanism of conversion, due to sulfhydryl modification and reversible with dithiothreitol (DTT), is potentially important but has not been well investigated. In this study rat liver and kidney were found to produce significant amounts of DTT-reversible XO during normothermic global ischemia. Formation of reversible XO precedes that of irreversible XO by approximately 0.5 h with a strong correlation (r = 0.92) existing between the rate of irreversible XO formation and the concentration of reversible XO. The formation of reversible XO is preceded by a depletion of glutathione with concentrations of glutathione during ischemia correlating (r = 0.85) with the observed concentration of reversible XO. While a large increase in the extent of liver damage occurs concurrently with conversion in an in vivo liver model of liver ischemia, an ischemia-reperfusion regimen (1 h of ischemia plus 0.5 h of reperfusion) that resulted in no conversion caused significant elevations in serum glutamic pyruvic transaminase and serum glutamic-oxaloacetic transaminase. Rats depleted of XO by tungsten dieting release 65% less enzyme after the same insult, suggesting that endogenous XO may also participate in the damage process independent of any conversion.

Animals↗