Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

MnO2 reacted with desferrioxamine B yielding a green, water-soluble complex, with absorption maxima at 315 and 635 nm whose extinction coefficients were 925 and 60 M-1 cm-1, respectively. Increasing the proportion of ligand to metal increased both color yield and ability to scavenge O2-, with maximal color yield and activity being achieved at a 1:1 ratio. The complex catalyzed the dismutation of O2- and 1 microM was equivalent to 1 unit of superoxide dismutase activity in the xanthine oxidase-cytochrome c assay. The complex thus exhibited approximately 0.1% as much activity as did the manganese-containing superoxide dismutase, on the basis of manganese content. The activity of the complex was not suppressed by bovine serum albumin or by the soluble proteins extracted from Lactobacillus plantarum. In contrast, the activities of Cu(II) complexes of salicylate or Gly-His-Lys were suppressed by these proteins.
 ...
PMID:A mimic of superoxide dismutase activity based upon desferrioxamine B and manganese(IV). 282 13

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.
 ...
PMID:Antiproteinases protect cultured lung endothelial cells from endotoxin injury. 284 19

Phosphate was reported to be an inhibitor of copper- and zinc-containing superoxide dismutase (SOD) [de Freitas, D.M., & Valentine, J.S. (1984) Biochemistry 23, 2079-2082]. Thus SOD activity, in 50 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) (pH 7.4), was decreased by approximately 50% when the assay was made 10 mM in phosphate, and the ionic strength was adjusted with sodium fluoride. The inhibitory effect of phosphate was attributed to the neutralization of the positive charge on the guanidino residue of Arg-141. We have reexamined the effects of phosphate inhibition of SOD and found that the enzyme has identical activity in phosphate or HEPES buffer when the ionic strength is adjusted with NaBr. The putative inhibitory effect of phosphate appears to have been due to fluoride inhibition of the superoxide generating system of xanthine/xanthine oxidase. We have confirmed this result by using a photochemical generation of O2- in addition to the enzymatic generation of O2-. Chemical modification of the lysine residues to homoarginines does not affect the activity of the enzyme and does not impart a phosphate sensitivity. Chemical modification with phenylglyoxal caused approximately 80% inactivation of the native enzyme and 90% inactivation of the O-methylisourea-modified enzyme. Our results suggest that phosphate does not inhibit the copper- and zinc-containing superoxide dismutase (Cu,Zn-SOD) beyond the expectations of its effect on ionic strength.
 ...
PMID:Phosphate inhibition of the copper- and zinc-containing superoxide dismutase: a reexamination. 302

The active site arginine-143 of human Cu,Zn superoxide dismutase has been replaced by lysine or by isoleucine. The mutant proteins were expressed at high levels in yeast, purified, and the amino acid substitution explored through the use of group specific reagents. The specific activities of these enzymes, measured by the xanthine oxidase/cytochrome c method and by using dry weight determination to establish protein concentration, were: native enzyme, 6570 units/mg; Lys-substituted enzyme, 2840 units/mg, Ile-substituted enzyme, 708 units/mg. The active site arginine thus plays an important, but not an essential, role in the catalytic process.
 ...
PMID:Examination of the role of arginine-143 in the human copper and zinc superoxide dismutase by site-specific mutagenesis. 311 54

Xanthine oxidase (EC 1.2.3.2) was purified from fresh cows' milk by differential centrifugation and hydroxylapatite chromatography in the absence of reducing agents and proteases. The purified isolate possessed an absorbance at 280 nm:absorbance at 450 nm ratio of 4.84; an absorbance (1 cm at 280 nm 1%) of 11.9; an activity:absorbance at 450 nm of 141, a specific activity of 3.59 units/mg; and detectable dehydrogenase activity. The enzyme preparation was obtained in a reversible oxidase form that could be partially converted to xanthine dehydrogenase in the presence of 10mM dithiothreitol or 1% mercaptoethanol. Amino acid analyses revealed that the enzyme was hydrophobic in nature and that lysine constituted its N-terminal residue. The protein contained 22 disulfide and 38 sulfhydryl groups, four of which were detectable in the undenatured protein complex. Discontinuous PAGE in the presence of selected dissociation agents did not result in further resolution. Sodium dodecyl sulfate-PAGE of the purified enzyme revealed a sharp zone with a molecular weight of 151,000 +/- 4000 (i.e., monomer). The purified enzyme exhibited oxidase activity in the presence of 6 M urea and following limited proteolysis by trypsin, chymotrypsin, plasmin, pancreatin, pepsin, and papain. Proteolyzed xanthine oxidase migrated as a single zone in polyacrylamide gels in the presence and absence of dissociating agents such as 1% mercaptoethanol and 6 M urea. Restricted digestion of xanthine oxidase by proteases was indicated by the presence of three major zones with molecular weights ranging from 85,000 to 100,000, 30,000 to 35,000, and 18,000 to 20,000 commonly observed in SDS gels. Amino acid profiles of the principal peptidyl fragments of trypsin-cleaved xanthine oxidase indicated their hydrophobic nature and lysine as the N-terminal residue for all fragments.
 ...
PMID:Characteristics of purified cows' milk xanthine oxidase and its submolecular characteristics. 339 6

L-Glutamic acid has been found to be a positive and L-lysine a negative modifier of the xanthine oxidase activity at the optimum pH (7.4) of the enzyme. Increase in pH was observed to be associated with a progressive decrease in the inhibition produced by L-lysine.
 ...
PMID:Amino acids: modifiers of xanthine oxidase activity. 678 Apr 61

Milk xanthine oxidase reacted with fluorodinitrobenzene resulting in the modification of two lysine residues with a 6-fold decrease in catalytic activity. Continued reaction with fluorodinitrobenzene up to a total of 11 dinitrophenyl residues/equivalent of enzyme-bound FAD resulted in no further decrease in activity. Stopped flow studies revealed that the modification perturbed the reduction of the enzyme by xanthine; this was 6-fold lower with modified than with native enzyme. The reaction of the reduced modified enzyme with oxygen was qualitatively and quantitatively the same as with native enzyme. One nitro group of each dinitrophenyl lysine residue is slowly reduced by xanthine; reduction of both nitro groups is achieved by dithionite. The two dinitrophenyl lysine reduces can be distinguished on the basis of their kinetics of reduction. One appears to be located on the protein surface and is reduced in an intermolecular reaction, while the other appears to be located in a pocket of the enzyme and is reduced in a slow intramolecular reaction.
 ...
PMID:Inhibition of milk xanthine oxidase by fluorodinitrobenzene. 680 72

The enzyme xanthine oxidase (XOD) has an affinity for heparin and can bind to cultured porcine aortic endothelial cells. We have reported that the exposure of human XOD (h-XOD) to the lysine-specific reagent trinitrobenzenesulfonic acid or the arginine-specific reagent phenylglyoxal caused it to lose its affinity for heparin-Sepharose. The heparin-binding sites in h-XOD are further studied in the present article. From a chymotryptic digest of cyanogen bromide fragmented h-XOD, two peptides with an affinity for heparin-HPLC, A-1 and A-2, were isolated. Amino acid sequence analysis showed that both peptides had lysine and/or arginine residues. The A-1 region may direct its charged side chains toward the solvent while burying its hydrophobic side chains against the hydrophobic inside, because the A-1 peptide forms a highly amphipathic structure. Peptide A-2 contains triple lysine residues and constitutes a hydrophilic region.
 ...
PMID:The heparin-binding site of human xanthine oxidase. 773 31

In this paper we demonstrate that in the absence of free metal ions, active oxygen species, generated by activated macrophages or xanthine/xanthine oxidase (XOD), carry out oxidative degradation of collagen fibrils type I in conjunction with proteases. The collagen degradation is completely prevented by ascorbate (AH2) but not by catalase. The free metal ion-independent collagen degradation is a two-step process: (i) oxidation of collagen and (ii) subsequent proteolytic cleavage of the oxidatively modified collagen. AH2 completely prevents collagen oxidation and thereby protects the collagen from subsequent proteolytic degradation. This is in contrast to free metal ion-catalyzed spontaneous fragmentation of collagen, which is accelerated by AH2 and inhibited by catalase (Kato, Y., Uchida, K., and Kawakishi, S. (1992) J. Biol. Chem. 267, 23646-23651). Studies using xanthine/XOD and model polypeptides, namely, poly-L-Pro, poly-L-hydroxyproline, poly-L-Lys, and poly(Pro-Gly-Pro) indicate that although O2-. is needed along with XOD, oxidation of model polypeptides appears to be a direct function of XOD iron, which is also stimulated by cytochrome P450.
 ...
PMID:Free metal ion-independent oxidative damage of collagen. Protection by ascorbic acid. 798 27

Oxygen-derived free radicals are known to take part in cardiac injury during post-ischemic reperfusion (I/R). Xanthine oxidase (XO) is closely associated with the generation of superoxide radicals. We have determined the distribution of XO in rat myocardium after ischemia (I) and I/R by immunocytochemical method using murine monoclonal antibody against XO (bovine milk) and by enzyme histochemistry (EHC) in situ. Frozen sections of periodate-lysine-paraformaldehyde (PLP) fixed myocardium after 15, 60 and 90 min ischemia and 15 min ischemia and 30 min reperfusion were processed for immunocytochemistry and EHC. In other experiments, rats were treated with allopurinol, an inhibitor of XO, and hearts were processed for immunocytochemistry. By immunoperoxidase and immunofluorescence methods, a deep staining of interstitial cells, capillary and small blood vessels was observed, but the staining intensity of these cells was increased after reperfusion, in comparison to the normal and ischemic heart tissue. In the electron microscope, an immunoperoxidase reaction product was seen in the cytoplasm of interstitial, endothelial and smooth muscle cells. Similarly, EHC studies by nitroblue tetrazolium staining showed an increase in enzymatic activity in the tissue after reperfusion. The allopurinol-treated I/R tissue exhibited reduced staining. The data suggest that XO activity increases during ischemia but intensifies after reperfusion. The enzyme is localized in interstitial cells, coronary vessel endothelium and smooth muscle cells. XO is constantly present in the interstitial cells of the myocardium and it is a new finding not previously reported. It is further suggested that myocardial interstitium may be one of the major sites where oxygen derived radicals are generated during ischemia.
 ...
PMID:Subcellular distribution of xanthine oxidase during cardiac ischemia and reperfusion: an immunocytochemical study. 832 24


1 2 3 4 Next >>