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)

In Klebsiella pneumoniae, NifL modulates the activity of the transcriptional activator NifA in response to combined nitrogen or external molecular oxygen. We recently showed that K. pneumoniae NifL is a flavoprotein which apparently senses oxygen through a redox-sensitive, conformational change. In order to study whether the nitrogen signal might be transmitted to NifA through a stable modification of NifL we characterized the redox properties of NifL synthesized in Escherichia coli in the presence of different nitrogen sources. FAD analyses showed that purified NifL carried FAD as cofactor independent of nitrogen and oxygen availability. The redox potential of NifL synthesized in the presence of ammonium was -277+/-5 mV at pH 8.0 and 25 degrees C, as determined by reduction with dithionite or with enzymatic reduction by xanthine oxidase in the presence of methyl viologen as redox mediator. When synthesized under nitrogen-limiting conditions, NifL showed a redox potential of -274+/-6 mV at pH 8.0 and 25 degrees C. Fully reduced NifL fractions, synthesized under either condition listed above, reoxidized rapidly in the presence of molecular oxygen. These results indicate that for NifL synthesized in E. coli, the redox potential of the NifL-bound FAD is not influenced by the nitrogen source. The two NifL fractions differed, however, in that a non-flavin specific absorbance at 420 nm was found only in NifL synthesized in the presence of ammonium.
...
PMID:NifL of Klebsiella pneumoniae: redox characterization in relation to the nitrogen source. 1035 Jun 21

Transforming growth factor (TGF)-beta1 is a growth factor involved in the mechanisms of lung repair and fibrosis that follow inflammatory processes. We sought to examine the link between the generation of reactive oxygen intermediates (ROI) or reactive nitrogen intermediates (RNI) by inflammatory cells and the expression of TGF-beta1 by alveolar epithelial cells. Exposure of the A549 lung epithelial cell line to either an ROI generating system (xanthine and xanthine oxidase) or an RNI donor (S-nitroso-N-acetyl-penicillamine [SNAP]) promoted a time- and dose-dependent increase in TGF-beta1 release, as measured by a specific enzyme-linked immunosorbent assay. At the peak, the levels of TGF-beta1 were twice the control values. The induction of TGF-beta1 release by ROI was blunted by catalase and unaffected by superoxide dismutase, indicating the involvement of hydrogen peroxide. The response was also blunted by 5, 6-dichloro-1-beta-D-ribofuranosyl benzimidazole (DRB), a specific RNA polymerase II inhibitor, and accompanied by a corresponding increase in TGF-beta1 messenger RNA, as measured by quantitative/competitive reverse transcription polymerase chain reaction, suggesting the involvement of transcriptional mechanisms and possibly other downstream mechanisms. In contrast, RNI-induced TGF-beta1 release was unaffected by DRB and blunted by the protein synthesis inhibitor cycloheximide, suggesting the involvement of translational and post-translational mechanisms. This response required cyclic guanosine monophosphate (cGMP)- mediated processes because (1) immunoreactive cGMP accumulated in the culture medium of SNAP-treated cells; (2) SNAP-induced TGF-beta1 release was blunted by KT 5823, an inhibitor of cGMP-dependent protein kinase; and (3) similar increase in TGF-beta1 release was obtained by cell exposure to membrane-permeable dibutyryl-cGMP or to atrial natriuretic factor, a known agonist of particulate guanylate cyclase. These data suggest that in vitro exposure of human alveolar epithelial cells to ROI and RNI enhances TGF-beta1 release through different mechanisms. In vivo, this control may constitute a molecular link between inflammatory and fibrotic processes.
...
PMID:Reactive oxygen and nitrogen intermediates increase transforming growth factor-beta1 release from human epithelial alveolar cells through two different mechanisms. 1038 1

In continuing studies of limb effects resulting from fetal exposure to N(G)-nitro-(L)-arginine methyl ester (L-NAME), we examined the early time course of vascular changes and the effectiveness of fetal intraamniotic injection. Vascular engorgement and hemorrhage occurred within 4 hr of L-NAME treatment on gestational day (gd) 17, and direct injection appeared to be as effective as maternal intraperitoneal injection in inducing limb hemorrhage. Further studies examined protein nitration and electron transport inhibition in tissues of exposed fetuses. L-NAME caused significant increases in nitrotyrosine (NT) formation in limb but not in heart or brain, and reduced electron transport rates in limb. Three agents, alpha-phenyl-N-t-butylnitrone (PBN), a radical trap and inhibitor of inducible nitric oxide synthase (iNOS), allopurinol, an inhibitor of xanthine oxidase, and aminoguanidine, a relatively specific inhibitor of iNOS, significantly moderated limb hemorrhage and protein nitration in distal limb. These results suggest that L-NAME works directly on the fetal limb vasculature and indicate a cytotoxic role for peroxynitrite, a potent oxidant and nitrating agent that is the reaction product of nitric oxide and superoxide anion radical. We propose that L-NAME and other vasoactive toxicants disrupt the fetal limb in a sequential process. Initially, nitric oxide (NO) is depleted, causing hemorrhage and edema in the limb. Within hours, iNOS is induced, resulting in cytotoxic tissue concentrations of NO and reactive nitrogen species that induce apoptosis and/or necrosis in the limb. We suggest that L-NAME exposure may serve as a model of vascular disruptive limb malformations.
...
PMID:Role of free radicals in the limb teratogenicity of L-NAME (N(G)-nitro-(L)-arginine methyl ester): a new mechanistic model of vascular disruption. 1047

The radical scavenging activity and the antioxidant content of fresh and air-dried tomatoes were investigated. Tomato halves were dried in a pilot-scale dryer under the following conditions: air temperature, 80 degrees C; air flow rate, 1.5 m/s; drying time, 400 min; final moisture, 25%. Carotenoid (lycopene, beta-carotene, lutein) and ascorbic acid were analyzed by HPLC with a spectrophotometric and an electrochemical detector, respectively. Total phenolics were determined by using the Folin-Ciocalteu reagent. The radical scavenging activity was studied in three model systems: (a) the xanthine oxidase and xanthine system, which generates superoxide radical and hydrogen peroxide; (b) the 3-morpholinosydnonimine system, which releases spontaneously superoxide radical and nitrogen monoxide, forming peroxynitrite; (c) the linoleic acid and CuSO(4) system, which promotes lipid peroxidation. These model systems allow the simulation of key reactions involved in the pathogenesis of certain chronic diseases and may be related to the in vivo activity of tomato antioxidants. Hence, these measurements can be used for optimizing tomato processing and storage. The drying process resulted in a decrease of ascorbic acid content, whereas phenol reagent reducing compounds increased. Carotenoid levels were substantially unchanged upon drying. Fresh and air-dried tomato extracts could act as radical scavengers both in the reactive oxygen species-mediated reactions and in lipid peroxidation. Drying affected the antioxidant effectiveness as measured in the xanthine/xanthine oxidase system, which was found to be the most sensitive method for the measurement of tomato antioxidant activity (lower I(50)) but retained the antioxidant effectiveness in the other two systems.
...
PMID:Evaluation of radical scavenging activity of fresh and air-dried tomatoes by three model reactions. 1055 29

In the vasculature, nitrosothiols derived from the nitric oxide (NO)-mediated S-nitrosation of thiols play an important role in the transport, storage, and metabolism of NO. The present study was designed to examine the reactions that promote the decomposition, formation, and distribution of extracellular nitrosothiols in the circulation. The disappearance of these species in plasma and whole blood was examined using a high-performance liquid chromatography method to separate low- and high-molecular weight nitrosothiols. We found that incubation of S-nitrosocysteine (CySNO) or S-nitrosoglutathione (GSNO) with human plasma resulted in a rapid decomposition of these nitrosothiols such that <10% of the initial concentration was recovered after 10-15 min. Neither metal chelators (DTPA, neocuproine), nor zinc chloride (glutathione peroxidase inhibitor), acivicin (gamma-glutamyl transpeptidase inhibitor), or allopurinol (xanthine oxidase inhibitor) inhibited the decomposition of GSNO. With both CySNO and GSNO virtually all NO was recovered as S-nitrosoalbumin (AlbSNO), suggesting the involvement of a direct transnitrosation reaction. Electrophilic attack of the albumin-associated thiols by reactive nitrogen oxides formed from the interaction of NO with O(2) was ruled out because one would have expected 50% yield of AlbSNO. Similar results were obtained in whole blood. The amount of S-nitrosohemoglobin recovered in the presence of 10 microM GSNO or CySNO was less than 100 nM taking into consideration the detection limit of the assay used. Our results suggest that serum albumin may act as a sink for low-molecular-weight nitrosothiols and as a modulator of NO(+) transfer between the vascular wall and intraerythrocytic hemoglobin.
...
PMID:Dynamic state of S-nitrosothiols in human plasma and whole blood. 1069 53

Reactive nitrogen species, including nitrogen oxides (N(2)O(3) and N(2)O(4)), peroxynitrite (ONOO(-)), and nitryl chloride (NO(2)Cl), have been implicated as causes of inflammation and cancer. We studied reactions of secondary amines with peroxynitrite and found that both N-nitrosamines and N-nitramines were formed. Morpholine was more easily nitrosated by peroxynitrite at alkaline pH than at neutral pH, whereas its nitration by peroxynitrite was optimal at pH 8.5. The yield of nitrosomorpholine in this reaction was 3 times higher than that of nitromorpholine at alkaline pH, whereas 2 times more nitromorpholine than nitrosomorpholine was formed at pH <7.5. For the morpholine-peroxynitrite reaction, nitration was enhanced by low concentrations of bicarbonate, but was inhibited by excess bicarbonate. Nitrosation was inhibited by excess bicarbonate. On this basis, we propose a free radical mechanism, involving one-electron oxidation by peroxynitrite of secondary amines to form amino radicals (R(2)N(*)), which react with nitric oxide ((*)NO) or nitrogen dioxide ((*)NO(2)) to yield nitroso and nitro secondary amines, respectively. Reaction of morpholine with NO(*) and superoxide anion (O(2)(*)(-)), which were concomitantly produced from spermine NONOate and by the xanthine oxidase systems, respectively, also yielded nitromorpholine, but its yield was <1% of that of nitrosomorpholine. NO(*) alone increased the extent of nitrosomorpholine formation in a dose-dependent manner, and concomitant production of O(2)(*)(-) inhibited its formation. Reactions of morpholine with nitrite plus HOCl or nitrite plus H(2)O(2), with or without addition of myeloperoxidase or horseradish peroxidase, also yielded nitration and nitrosation products, in yields that depended on the reactants. Tyrosine was nitrated easily by synthetic peroxynitrite, by NaNO(2) plus H(2)O(2) with myeloperoxidase, and by NaNO(2) plus H(2)O(2) under acidic conditions. Nitrated secondary amines, e.g., N-nitroproline, could be identified as specific markers for endogenous nitration mediated by reactive nitrogen species.
...
PMID:Formation of N-nitrosamines and N-nitramines by the reaction of secondary amines with peroxynitrite and other reactive nitrogen species: comparison with nitrotyrosine formation. 1077 31

We describe the synthesis and biological applications of a novel nitrogen-15-labeled nitrone spin trap, 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide ([(15)N]EMPO) for detecting superoxide anion. Superoxide anion generated in xanthine/xanthine oxidase (100 nM min(-1)) and NADPH/calcium-calmodulin/nitric oxide synthase systems was readily detected using EMPO, a nitrone analog of 5,5'-dimethyl-1-pyrroline N-oxide (DMPO). Unlike DMPO-superoxide adduct (DMPO-OOH), the superoxide adduct of EMPO (EMPO-OOH) does not spontaneously decay to the corresponding hydroxyl adduct, making spectral interpretation less confounding. Although the superoxide adduct of 5-(diethoxyphosphoryl)-5-methyl-pyrroline N-oxide is more persistent than EMPO-OOH, the electron spin resonance spectra of [(14)N]EMPO-OOH and [(15)N]EMPO-OOH are less complex and easier to interpret. Potential uses of [(15)N]EMPO in elucidating the mechanism of superoxide formation from nitric oxide synthases, and in ischemia/reperfusion injury are discussed.
...
PMID:Detection of superoxide anion using an isotopically labeled nitrone spin trap: potential biological applications. 1080 59

Free radicals have previously been shown to kill the immature stages of the trematode, Schistosoma mansoni but their effect on newly excysted juvenile (NEJ) flukes of Fasciola hepatica has not been established. Using acetaldehyde and xanthine oxidase to chemically generate reactive oxygen intermediates (ROI), up to 61% of NEJ were killed but only when exposed to high levels of ROI. At low concentrations of acetaldehyde and xanthine oxidase as sources of reactive oxygen intermediates, only 6-29% of NEJ were killed compared with 70-92% of schistosomula. Incubation with lipopolysaccharide (LPS)-stimulated rat peritoneal lavage cells (PLCs) killed only 7-15% of NEJ whereas 78-87% of schistosomula were killed under the same conditions by a mechanism dependent on the production of reactive nitrogen intermediates. Relative to immature and adult parasites, NEJ expressed 2.5-20-fold lower levels of superoxide dismutase and glutathione S-transferase but no catalase activity was detected. Incubation of NEJ with inhibitors of peroxidases and glutathione metabolism increased the mean killing of NEJ by LPS-stimulated rat PLCs to 40-75%. These results demonstrate that, in comparison to schistosomula of S. mansoni, NEJ of F. hepatica are relatively resistant to killing by free radicals and this resistance could, in part, be due to the activity of oxidant scavenger enzymes of NEJ.
...
PMID:Juvenile Fasciola hepatica are resistant to killing in vitro by free radicals compared with larvae of Schistosoma mansoni. 1084 8

We determined placental tissue levels, production rates, and secretion rates of isoprostanes for placentas obtained from women with normal pregnancies and women with preeclampsia, a hypertensive disorder of pregnancy. Isoprostanes are markers of oxidative stress that exert biological actions such as vasoconstriction. Placental tissue was rinsed and immediately frozen in liquid nitrogen to determine tissue levels of total and free isoprostane. Placental tissue pieces were also incubated in serum-free DMEM for 48 h at 37 degrees C in 95% air/5% CO(2) to determine production rates. Isolated placental cotyledons were perfused for the determination of secretion rates. All samples were analyzed by EIA for isoprostane using an antibody specific for 8-Iso-PGF(2) (15-F(2t)-IsoP). In addition, medium samples were analyzed for malondialdehyde (MDA), a breakdown product of lipid peroxidation. We found that tissue levels of free isoprostane and total isoprostane (free plus esterified forms) were significantly higher for preeclamptic placentas than for normal placentas. Concentrations of isoprostane and MDA in the medium increased progressively during 48 h of incubation of placental explants. At 48 h of incubation, the mean concentrations of both isoprostane and MDA were significantly higher for the placentas from preeclamptic women than for the placentas from normal pregnant women. Concentrations of MDA were highly correlated with those of isoprostane. Induction of oxidative stress with xanthine plus xanthine oxidase increased placental production of isoprostane by normal tissue to a level similar to that of preeclamptic tissue. Placental secretion of isoprostane was eightfold greater toward the maternal side of the placenta than toward the fetal side, and was increased sixfold on the maternal side and twofold on the fetal side by inducing oxidative stress with t-butyl hydroperoxide. This study presents new information that isoprostanes are formed and secreted by the human placenta and provides convincing evidence that oxidative stress and lipid peroxidation are abnormally increased in placentas of preeclamptic women.
...
PMID:Placental isoprostane is significantly increased in preeclampsia. 1087 21

Oxidative modification of low density lipoprotein (LDL) appears to play an important role in atherogenesis. Although the precise mechanisms of LDL oxidation in vivo are unknown, several lines of evidence implicate myeloperoxidase and reactive nitrogen species, in addition to ceruloplasmin and 15-lipoxygenase. Myeloperoxidase generates a number of reactive species, including hypochlorous acid, chloramines, tyrosyl radicals, and nitrogen dioxide. These reactive species oxidize the protein, lipid, and antioxidant components of LDL. Modification of apolipoprotein B results in enhanced uptake of LDL by macrophages with subsequent formation of lipid-laden foam cells. Nitric oxide synthases produce nitric oxide and, under certain conditions, superoxide radicals. Numerous other sources of superoxide radicals have been identified in the arterial wall, including NAD(P)H oxidases and xanthine oxidase. Nitric oxide and superoxide readily combine to form peroxynitrite, a reactive nitrogen species capable of modifying LDL. In this review, we examine the reaction pathways involved in LDL oxidation by myeloperoxidase and reactive nitrogen species and the potential protective effects of the antioxidant vitamins C and E.
...
PMID:Oxidation of LDL by myeloperoxidase and reactive nitrogen species: reaction pathways and antioxidant protection. 1089 8


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

---