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

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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)

Tyrosinase isolated from cultured human melanoma cells was studied for tyrosine oxygenation activity. L-Tyrosine and D-tyrosine were used as substrates and dopa was measured with HPLC and electrochemical detection as the product of oxygenation. Incubations were performed in the presence or absence of dopamine as co-substrate. Oxygenation of L-tyrosine occurred only in the presence of dopamine as co-substrate. No oxygenation of D-tyrosine was found, and we conclude that human tyrosinase is characterised by exclusive specificity for the L-isomer of tyrosine in its oxygenase function. It has recently been suggested that superoxide anion is a preferential oxygen substrate for human tyrosinase. Incubations were therefore performed with L- and D-tyrosine, human tyrosine, and xanthine/xanthine oxidase in the system, generating superoxide anion and hydrogen peroxide. Considerable formation of dopa was observed, but the quantity was the same irrespective of whether D-tyrosine or L-tyrosine was used as the substrate. Furthermore, formation of dopa occurred in a xanthine/xanthine oxidase system when bovine serum albumin (BSA) was substituted for tyrosinase. Our results provide no evidence that superoxide anion is an oxygen substrate for human tyrosinase. In the incubate containing xanthine/xanthine oxidase, catalase completely inhibited dopa formation, and superoxide dismutase and mannitol each strongly inhibited dopa formation. The results are compatible with hydroxyl radicals being responsible for the formation of dopa, since such radicals may be secondarily formed in the presence of superoxide anion and hydrogen peroxide.
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PMID:Enzymatic and non-enzymatic oxygenation of tyrosine. 885 72

This study concerns the controversial problem of whether the TNF-alpha (TNF) induces a respiratory burst in human neutrophils in suspension. The results have shown that in these cells TNF induces a classical respiratory burst. In fact, the production of oxygen free radicals 1) is linked to the translocation of NADPH oxidase components from cytosol to the plasma membrane, 2) does not take place in neutrophils from a patient lacking the cytochrome b558, and 3) does not involve other sources such as mitochondrial respiratory chain or xanthine oxidase. Signal transduction studies have demonstrated that this respiratory burst 1) is not accompanied by calcium transients, stimulation of phosphoinositide turnover, and phospholipase D activity (moreover, this burst is associated with the stimulation of the activity of phospholipase A2, but not of sphingomyelinase); 2) is strictly dependent on activation of tyrosine kinases, which is functional to the translocation to the plasma membrane of the cytosolic NADPH oxidase component rac; and 3) is dependent on the integrity of the cytoskeleton because it is completely suppressed by cytochalasin B. The integrity of the cytoskeleton is required for a full translocation of all the NADPH oxidase components and for an optimal activation of tyrosine kinases, but not for phospholipase A2 activation. Taken together, these findings demonstrate that TNF activates the NADPH oxidase through stimulation of tyrosine kinases, whose function is cytoskeleton-dependent, and raise the problem of whether the activation of this respiratory burst involves signals arising from TNF-activated beta2 integrins.
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PMID:Mechanisms of stimulation of the respiratory burst by TNF in nonadherent neutrophils: its independence of lipidic transmembrane signaling and dependence on protein tyrosine phosphorylation and cytoskeleton. 890 41

1. The possible mechanisms of the inhibitory effect of ethyl 2-(3-hydroxyanilino)-4-oxo-4,5-dihydrofuran-3-carboxylate (HAJ11) on the respiratory burst of rat neutrophils in vitro was investigated. 2. HAJ11 caused a reversible and a concentration-dependent inhibition of formyl-Met-Leu-Phe (fMLP)-induced superoxide anion (O2.-) generation (IC50 4.9 +/- 0.7 microM) and O2 consumption (IC50 4.9 +/- 1.5 microM). Concanavalin A (Con A)- and NaF-induced O2.- generation were also suppressed by HAJ11. However, HAL11 was a weak inhibitor of the phorbol 12-myristate 13-acetate (PMA)-induced responses. 3. HAJ11 did not scavenge the /2.- generation in the xanthine-xanthine oxidase system and dihydroxyfumaric acid (DHF) autoxidation. 4. HAJ11 showed no activity on fMLP-induced inositol phosphates formation and [Ca2+]i elevation in intact neutrophils. In addition, HAJ11 had no effect on neutrophil cytosolic phospholipase C (PLC) activity. 5. HAJ11 reduced fMLP-induced phosphatidic acid (PA) (IC50 29.1 +/- 6.5 microM) and phosphatidylethanol (PE+) (IC50 22.6 +/- 1.9 microM) formation in a concentration-dependent manner. HAJ11 also reduced protein tyrosine phosphorylation in neutrophils stimulated by fMLP. 6. HAJ11 was a weak inhibitor of neutrophil cytosolic protein kinase C (PKC) activity, and had a negligible effect on brain PKC. Cellular cyclic nucleotides levels were not altered by HAJ11. In addition, HAJ11 did not affect protein kinase A (PKA) activity. 7. HAJ11 had not effect on the O2.- generation of PMA-activated and arachidonic acid (AA)-activated NADPH oxidase preparations. 8. Taken together these results indicate that the inhibition of respiratory burst by HAJ11 probably mainly occurs through inhibition of protein tyrosine phosphorylation and phospholipase D (PLD) activity.
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PMID:Inhibition by HAJ11 of respiratory burst in neutrophils and the involvement of protein tyrosine phosphorylation and phospholipase D activation. 911 3

Regulation of induced nitric oxide synthase (NOS) in isolated rat hepatocytes is poorly understood. The specific protein tyrosine kinase inhibitor genistein was used to determine if NOS induction is dependent on protein tyrosine kinase activation. Genistein inhibited tumor necrosis factor-alpha (TNF-alpha)-stimulated induction of NOS activity and NOS protein in a dose-dependent manner. Genistein also impaired TNF-alpha-induced NOS mRNA accumulation, suggesting protein tyrosine kinase regulation of NOS induction occurred at the level of transcription-translation. Like TNF-alpha, genistein inhibited induction of NOS protein by a second proinflammatory cytokine, interleukin-1beta, suggesting similar activation mechanisms by proinflammatory cytokines. NOS induction by other stimuli, including phorbol 12-myristate 13-acetate and the superoxide-generating system xanthine/xanthine oxidase, was also inhibited by genistein. Finally, cytokine-stimulated protein tyrosine kinase activity in hepatocytes was demonstrated by increased tyrosine phosphorylation of five high molecular mass protein bands. Genistein inhibited this cytokine-induced phosphotyrosine increase. The commonality of genistein inhibition suggests that protein tyrosine kinase activity is critical for NOS induction by a variety of stimuli.
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PMID:Protein tyrosine kinase activity regulates nitric oxide synthase induction in rat hepatocytes. 912 43

We have expressed, purified, and analyzed the iron-containing superoxide dismutase (FeSOD) of Escherichia coli with mutations directed at tyrosine position 34 to introduce phenylalanine (SODY34F), serine (SODY34S), or cysteine (SODY34C). FeSOD and mutant enzymes were purified from SOD-deficient cells using a GST-FeSOD fusion protein intermediate which was subsequently cleaved with thrombin and repurified. Specific activities were measured using the xanthine-xanthine oxidase method and gave 3148 u/mg for wild-type FeSOD. The SODY34S mutation virtually inactivates the enzyme (42 u/mg); mutation to cysteine greatly reduces activity (563 u/mg), but the SODY34F mutant retains nearly 40% of the activity of wild type (1205 u/mg). Fusion protein intermediates were also shown to be active and were demonstrated to protect SOD-deficient E. coli cells from the induced effects of oxidative stress, with growth rates directly proportional to the specific activities of the expressed mutant enzymes. SODY34F exhibited decreased thermal stability, reduced activity at high pH, and a pronounced increase in sensitivity to the inhibitor sodium azide compared with wild-type FeSOD. These results suggest that tyrosine at position 34 is multifunctional and plays a structural role (probably through hydrogen bonding to glutamine at position 69) in maintaining the integrity of the active site, a stabilizing role at high pH, and a steric role in obstructing access to the active site of both substrate and inhibitor molecules.
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PMID:The conserved residue tyrosine 34 is essential for maximal activity of iron-superoxide dismutase from Escherichia coli. 912 14

1. The possible mechanisms of action of the inhibitory effect of abruquinone A on the respiratory burst in rat neutrophils in vitro was investigated. 2. Abruquinone A caused an irreversible and a concentration-dependent inhibition of formylmethionylleucyl-phenylalanine (fMLP) plus dihydrocytochalasin B (CB)- and phorbol 12-myristate 13-acetate (PMA)-induced superoxide anion (O2.-) generation with IC50 values of 0.33 +/- 0.05 microgram ml-1 and 0.49 +/- 0.04 microgram ml-1, respectively. 3. Abruquinone A also inhibited O2 consumption in neutrophils in response to fMLP/CB and PMA. However, abruquinone A did not scavenge the generated O2.- in xanthine-xanthine oxidase system and during dihydroxyfumaric acid (DHF) autoxidation. 4. Abruquinone A inhibited both the transient elevation of [Ca2+]i in the absence of [Ca2+]o (IC50 7.8 +/- 0.2 micrograms ml-1) and the generation of inositol trisphosphate (IP3) (IC50 10.6 +/- 2.0 micrograms ml-1) in response to fMLP. 5. Abruquinone A did not affect the enzyme activaties of neutrophil cytosolic protein kinase C (PKC) and porcine heart protein kinase A (PKA). 6. Abruquinone A had no effect on intracellular guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels but decreased the adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels. 7. The cellular formation of phosphatidic acid (PA) and phosphatidylethanol (PEt) induced by fMLP/ CB was inhibited by abruquinone A with IC50 values of 2.2 +/- 0.6 micrograms ml-1 and 2.5 +/- 0.3 micrograms ml-1, respectively. Abruquinone A did not inhibit the fMLP/CB-induced protein tyrosine phosphorylation but induced additional phosphotyrosine accumulation on proteins of 73-78 kDa in activated neutrophils. 8. Abruquinone A inhibited both the O2.- generation in PMA-activated neutrophil particulate NADPH oxidase (IC50 0.6 +/- 0.1 microgram ml-1) and the iodonitrotetrazolium violet (INT) reduction in arachidonic acid (AA)-activated cell-free system (IC50 1.5 +/- 0.2 micrograms ml-1) 9. Collectively, these results indicate that the inhibition of respiratory burst in rat neutrophils by abruquinone A is mediated partly by the blockade of phospholipase C (PLC) and phospholipase D (PLD) pathways, and by suppressing the function of NADPH oxidase through the interruption of electron transport.
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PMID:Cellular localization of the inhibitory action of abruquinone A against respiratory burst in rat neutrophils. 913 99

1. The ability of acetylshikonin to inhibit the respiratory burst in rat neutrophils was characterized and the underlying mechanism of action was also assessed in the present study. 2. Acetylshikonin caused an irreversible and a concentration-dependent inhibition of formylmethionylleucyl-phenylalanine (fMLP) plus dihydrocytochalasin B (CB)- and phorbol 12-myristate 13-acetate (PMA)-induced superoxide anion (O2.-) generation with IC50 values of 0.48 +/- 0.03 and 0.39 +/- 0.03 microM, respectively. Acetylshikonin also inhibited the O2 consumption in neutrophils in response to fMLP/CB as well as to PMA. 3. Acetylshikonin did not scavenge the generated O2.- in the xanthine-xanthine oxidase system or during dihydroxyfumaric acid (DHF) autoxidation but, on the contrary, acetylshikonin enhanced the O2.- generation in these cell-free oxygen radical generating systems. 4. Acetylshikonin inhibited the formation of inositol trisphosphate (IP3) (39.0 +/- 7.8% inhibition at 10 microM, P < 0.05) in neutrophils in response to fMLP. 5. Both the neutrophil cytosolic protein kinase C (PKC) activity and the PMA-induced PKC associated with the membrane were unaffected by acetylshikonin. 6. Acetylshikonin did not affect the porcine heart protein kinase A (PKA) activity. Upon exposure to acetylshikonin, the cellular cyclic AMP level was decreased in neutrophils in response to fMLP. 7. The cellular formation of phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt) induced by fMLP/CB were inhibited by acetylshikonin (60.1 +/- 7.3 and 63.2 +/- 10.5% inhibition, respectively, at 10 microM, both P < 0.05). Moreover, acetylshikonin attenuated the fMLP/CB-induced protein tyrosine phosphorylation (about 90% inhibition at 1 microM). 8. In PMA-activated neutrophil particulate NADPH oxidase preparations, acetylshikonin did not inhibit, but enhanced, the O2.- generation in the presence of NADPH. However, acetylshikonin decreased the membrane associated p47phox in PMA-activated neutrophils (about 60% inhibition at 1 microM). 9. Collectively, these results suggest that the attenuation of protein tyrosine phosphorylation and a failure in the assembly of a functional NADPH oxidase complex probably contribute predominantly to the inhibition of respiratory burst in neutrophils by acetylshikonin. In contrast, the blockade of phospholipase C (PLC) and phospholipase D (PLD) pathways play only a minor role in this respect.
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PMID:Investigation of the inhibition by acetylshikonin of the respiratory burst in rat neutrophils. 917 81

Norathyriol, aglycone of a xanthone C-glycoside mangiferin isolated from Tripterospermum lanceolatum, concentration dependently inhibited the formylmethionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O2.-) generation and O2 consumption in rat neutrophils. In cell-free oxygen radical generating system, norathyriol inhibited the O2.- generation during dihydroxyfumaric acid (DHF) autoxidation and in hypoxanthine-xanthine oxidase system. fMLP-induced transient elevation of [Ca2/]i and the formation of inositol trisphosphate (IP3) were significantly inhibited by norathyriol (30 microM) (about 30 and 46% inhibition, respectively). Norathyriol concentration dependently suppressed the neutrophil cytosolic phospholipase C (PLC). In contrast with the marked attenuation of fMLP-induced protein tyrosine phosphorylation (about 70% inhibition at 10 microM norathyriol), norathyriol only slightly modulated the phospholipase D (PLD) activity as determined by the formation of phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt). Norathyriol did not modulate the intracellular cyclic AMP level. In the presence of NADPH, the phorbol 12-myristate 13-acetate (PMA)-activated particulate NADPH oxidase activity was suppressed by norathyriol in a concentration-dependent manner and the inhibition was noncompetitive with respect to NADPH. Norathyriol inhibited the iodonitrotetrazolium violet (INT) reduction in arachidonic acid (AA)-activated cell-free NADPH oxidase system at the same concentration range as those used in the suppression of PMA-activated particulate NADPH oxidase activity. Taken together, these results suggest that the scavenging ability of norathyriol contributes to the reduction of generated O2.-, however, the inhibition of O2.- generation from neutrophils by norathyriol is attributed to the blockade of PLC pathway, the attenuation of protein tyrosine phosphorylation, and to the suppression of NADPH oxidase through the interruption of electrons transport.
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PMID:Examination of the inhibitory effect of norathyriol in formylmethionyl-leucyl-phenylalanine-induced respiratory burst in rat neutrophils. 935 47

Reactive oxygen species (ROS) have been suggested to act as cellular messengers that mediate signal transduction cascades in various cell types. However, little is known about their role in this capacity in the nervous system. We have begun to investigate the role of ROS, and that of nitric oxide (NO), in mediating mitogen-activated protein kinase (MAPK) signaling in rat hippocampal slices. Our studies have revealed that direct exposure of hippocampal slices to hydrogen peroxide, xanthine/xanthine oxidase (a superoxide-generating system), sodium nitroprusside (an NO donor compound), S-nitroso-N-acetylpenicillamine (an NO donor compound), or 3-morpholinosydnonimine (a compound that produces NO and superoxide) results in an enhancement in tyrosine phosphorylation of several proteins, including proteins with apparent molecular masses of 42 and 44 kDa. We investigated the possibility that these proteins correspond to the active forms of p42 MAPK and p44 MAPK. Hippocampal slices exposed to various ROS and NO donors resulted in increases in levels of the active forms of both p42 MAPK and p44 MAPK. The ROS- and NO-enhanced tyrosine phosphorylation and activation of p42 MAPK and p44 MAPK were inhibited by pretreatment with the antioxidant N-acetyl-L-cysteine. Our observations indicate that ROS and NO can mediate protein tyrosine phosphorylation and MAPK signaling in the hippocampus via a redox-sensitive mechanism and suggest a potential cellular mechanism for their effects in the nervous system.
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PMID:Stimulation of p42 and p44 mitogen-activated protein kinases by reactive oxygen species and nitric oxide in hippocampus. 948 20

Human lymphocytes were challenged with reactive oxygen species (ROS) generated by xanthine/xanthine oxidase leading to an increase in tyrosine phosphorylation, together with an increase in tyrosine phosphatase activity. In the presence of 50 microM vanadate and xanthine/xanthine oxidase, tyrosine phosphatase activity was inhibited and a marked increase in tyrosine phosphorylation was observed. The addition of catalase abolished the increase in tyrosine phosphorylation while the addition of superoxide dismutase had no effect. This suggests that vanadate together with hydrogen peroxide derived from xanthine/xanthine oxidase activity, interact to produce an agent that is an effective inhibitor of tyrosine phosphatase activity. When human lymphocytes were challenged with xanthine/xanthine oxidase in the presence of 50 microM CuCl2, an increase in both tyrosine phosphatase and kinase activity was observed. Cupric ions inhibited xanthine oxidase activity by 84%; neither superoxide or hydroxyl radicals could be detected, but traces of hydrogen peroxide were detected in the medium. We conclude that unbound metals can interact with ROS and readily influence signalling mechanisms in human lymphocytes.
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PMID:Free radical stimulation of tyrosine kinase and phosphatase activity in human peripheral blood mononuclear cells. 953 75


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