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

Nitroreductase enzymes generally catalyze the reduction of nitroaromatic compounds to the corresponding amines. In contrast, ferredoxin NADP oxidoreductase (FNR), glutathione reductase, xanthine oxidase, and cytochrome c reductase catalyze the NADPH dependent elimination of the nitramine nitro group from 2,4,6-trinitrophenylmethylnitramine to form N-methylpicramide (NMP). Nitrite elimination was inhibited under aerobic conditions. Our results suggest that under aerobic conditions, tetryl is enzymatically reduced to the nitroanion radical which is then involved in the reduction of molecular oxygen. Under anaerobic conditions, the radical is reduced to NMP and nitrite is eliminated.
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PMID:Elimination of nitrite from the explosive 2,4,6-trinitrophenylmethylnitramine (tetryl) catalyzed by ferredoxin NADP oxidoreductase from spinach. 860 4

A specific dehydrogenase, different from nicotinic acid hydroxylase, was induced during growth of Eubacterium barkeri on xanthine. The protein designated as xanthine dehydrogenase was enriched 39-fold to apparent homogeneity using a three-step purification scheme. It exhibited an NADP-dependent specific activity of 164 micromol xanthine oxidized per min and per mg of protein. In addition it showed an NADPH-dependent oxidase and diaphorase activity. A molecular mass of 530 kDa was determined for the native enzyme and SDS/PAGE revealed three types of subunits with molecular masses of 17.5, 30 and 81 kDa indicating a dodecameric native structure. Molybdopterin was identified as the molybdenum-complexing cofactor using activity reconstitution experiments and fluorescence measurements after KI/I2 oxidation. The molecular mass of the cofactor indicated that it is of the dinucleotide type. The enzyme contained iron, acid-labile sulfur, molybdenum, tungsten, selenium and FAD at molar ratios of 17.5, 18.4, 2.3, 1.1, 0.95 and 2.8 per mol of native enzyme. Xanthine dehydrogenase was inactivated upon incubation with arsenite, cyanide and different purine analogs. Reconstitution experiments of xanthine dehydrogenase activity by addition of selenide and selenite performed with cyanide-inactivated enzyme and with chloramphenicol-treated cells, respectively, indicated that selenium is not attached to the protein in a covalently bound form such as selenocysteine.
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PMID:Selenium-containing xanthine dehydrogenase from Eubacterium barkeri. 1049 Nov 34

Cell-free extract prepared from a mixed culture consisting of strains belonging to the genera Klebsiella and Rhodococcus grown in the presence of caffeine contains a novel enzyme, caffeine (1,3, 7-trimethylxanthine) oxidase which catalyzes the oxidation of caffeine at the C-8 position to produce 1,3,7-trimethyluric acid. The enzyme was purified to homogeneity by a combination of ion-exchange and hydrophobic column chromatographies. Both native and SDS/PAGE of the purified enzyme showed a single protein band and the subunit molecular mass of the protein was determined to be 85 kDa. Dichlorophenol indophenol and cytochrome c served as good electron acceptors but NAD and NADP did not. Caffeine served as the best substrate with an apparent K(m) of 11.4 microM. various analogues of theobromine were also effective substrates for caffeine oxidase. The activity was inhibited by o-phenanthroline, H(2)O(2), and methanol, but salicylate, thiol-group blocking reagents, and sodium arsenite, the known xanthine oxidase inhibitors, did not inhibit the reaction. The spectral characteristics of the purified enzyme suggest that it is a flavoprotein containing non-heme iron.
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PMID:Purification and partial characterization of caffeine oxidase--A novel enzyme from a mixed culture consortium. 1049 16

The effect of growing pea plants with 50 microM CdCl2 on the activated oxygen metabolism was studied at subcellular level in peroxisomes isolated from pea leaves. Cadmium treatment produced proliferation of peroxisomes as well as an increase in the content of H2O2 in peroxisomes from pea leaves, but in peroxisomal membranes no significant effect on the NADH-dependent O2*- production was observed. The rate of lipid peroxidation of membranes was slightly decreased in peroxisomes from Cd-treated plants. This could be due to the Cd-induced increase in the activity of some antioxidative enzymes involved in H2O2 removal, mainly ascorbate peroxidase and glutathione reductase, as well as the NADP-dependent dehydrogenases present in these organelles. The activity of xanthine oxidase did not experiment changes by Cd treatment and this suggests that O2*- production in the peroxisomal matrix is not involved in Cd toxicity. This was supported by the absence of changes in plants treated with Cd in the Mn-SOD activity, responsible for O2*- removal in the peroxisomal matrix. Results obtained indicate that toxic Cd levels induce imbalances in the activated oxygen metabolism of pea leaf peroxisomes, but its main effect is an enhancement of the H2O2 concentration of these organelles. Peroxisomes respond to Cd toxicity by increasing the activity of antioxidative enzymes involved in the ascorbate-glutathione cycle and the NADP-dependent dehydrogenases located in these organelles.
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PMID:Cadmium toxicity and oxidative metabolism of pea leaf peroxisomes. 1069 37

Peroxisomes are subcellular organelles with an essentially oxidative type of metabolism. Like chloroplasts and mitochondria, plant peroxisomes also produce superoxide radicals (O2*(-)) and there are, at least, two sites of superoxide generation: one in the organelle matrix, the generating system being xanthine oxidase, and another site in the peroxisomal membranes dependent on NAD(P)H. In peroxisomal membranes, three integral polypeptides (PMPs) with molecular masses of 18, 29 and 32 kDa have been shown to generate radicals O2*(-). Besides catalase, several antioxidative systems have been demonstrated in plant peroxisomes, including different superoxide dismutases, the ascorbate-glutathione cycle, and three NADP-dependent dehydrogenases. A CuZn-SOD and two Mn-SODs have been purified and characterized from different types of peroxisomes. The four enzymes of the ascorbate-glutathione cycle (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase) as well as the antioxidants glutathione and ascorbate have been found in plant peroxisomes. The recycling of NADPH from NADP(+) can be carried out in peroxisomes by three dehydrogenases: glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and isocitrate dehydrogenase. In the last decade, different experimental evidence has suggested the existence of cellular functions for peroxisomes related to reactive oxygen species (ROS), but the recent demonstration of the presence of nitric oxide synthase (NOS) in plant peroxisomes implies that these organelles could also have a function in plant cells as a source of signal molecules like nitric oxide (NO*), superoxide radicals, hydrogen peroxide, and possibly S-nitrosoglutathione (GSNO).
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PMID:Reactive oxygen species, antioxidant systems and nitric oxide in peroxisomes. 1199 74

The major insecticide imidacloprid (IMI) is known to be metabolized by human cytochrome P450 3A4 with NADPH by imidazolidine hydroxylation and dehydrogenation to give 5-hydroxy-imidacloprid and the olefin, respectively, and by nitroimine reduction and cleavage to yield the nitrosoimine, guanidine, and urea derivatives. More extensive metabolism by human or rabbit liver microsomes with NADPH or rabbit liver cytosol without added cofactor reduces the IMI N-nitro group to an N-amino substituent, i.e., the corresponding hydrazone. A major metabolite on incubation of IMI in the human microsome-NADPH system is tentatively assigned by LC/MS as a 1,2,4-triazol-3-one derived from the hydrazone; the same product is obtained on reaction of the hydrazone with ethyl chloroformate. The hydrazone and proposed triazolone are considered here together (referred to as the hydrazone) for quantitation. Only a portion of the microsomal reduction and cleavage of the nitroimine substituent is attributable to a CYP450 enzyme. The cytosolic enzyme conversion to the hydrazone is inhibited by added cofactors (NAD > NADH > NADP > NADPH) and enhanced by an argon instead of an air atmosphere. The responsible cytosolic enzyme(s) does not appear to be DT-diaphorase (which is inhibited by several neonicotinoids), aldose reductase, aldehyde reductase, or xanthine oxidase. However, the cytosolic metabolism of IMI is inhibited by several aldo-keto-reductase inhibitors (i.e., alrestatin, EBPC, Ponalrestat, phenobarbital, and quercetin). Other neonicotinoids with nitroimine, nitrosoimine, and nitromethylene substituents are probably also metabolized by "neonicotinoid nitro reductase(s)" since they serve as competitive substrates for [(3)H]IMI metabolism.
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PMID:Neonicotinoid insecticides: reduction and cleavage of imidacloprid nitroimine substituent by liver microsomal and cytosolic enzymes. 1223 Apr 9

In plant cells, as in most eukaryotic organisms, peroxisomes are probably the major sites of intracellular H2O2 production, as a result of their essentially oxidative type of metabolism. Like mitochondria and chloroplasts, peroxisomes also produce superoxide radicals (O2*-) and there are, at least, two sites of superoxide generation: one in the organelle matrix, the generating system being xanthine oxidase, and another site in the peroxisomal membranes dependent on NAD(P)H. In peroxisomal membranes, three integral polypeptides (PMPs) with molecular masses of 18, 29, and 32 kDa have been shown to generate O2*- radicals. Besides catalase, several antioxidative systems have been demonstrated in plant peroxisomes, including different superoxide dismutases, the four enzymes of the ascorbate-glutathione cycle plus ascorbate and glutathione, and three NADP-dependent dehydrogenases. A CuZn-SOD and two Mn-SODs have been purified and characterized from different types of plant peroxisomes. The presence of the enzyme nitric oxide synthase (NOS) and its reaction product, nitric oxide (NO*), has been recently demonstrated in plant peroxisomes. Different experimental evidence has suggested that peroxisomes have a ROS-mediated cellular function in leaf senescence and in stress situations induced by xenobiotics and heavy metals. Peroxisomes could also have a role in plant cells as a source of signal molecules like NO*, O2*- radicals, H2O2, and possibly S-nitrosoglutathione (GSNO). It seems reasonable to think that a signal molecule-producing function similar to that postulated for plant peroxisomes could also be performed by human, animal and yeast peroxisomes, where research on oxy radicals, antioxidants and nitric oxide is less advanced than in plant peroxisomes.
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PMID:Plant peroxisomes, reactive oxygen metabolism and nitric oxide. 1274 89

Pepper is a vegetable of importance in human nutrition. Currently, one of the most interesting properties of natural products is their antioxidant content. In this work, the purification and characterisation of peroxisomes from fruits of a higher plant was carried out, and their antioxidative enzymatic and non-enzymatic content was investigated. Green and red pepper fruits (Capsicum annuum L., type Lamuyo) were used in this study. The analysis by electron microscopy showed that peroxisomes from both types of fruits contained crystalline cores which varied in shape and size, and the presence of chloroplasts and chromoplasts in green and red pepper fruits, respectively, was confirmed. Peroxisomes were purified by differential and sucrose density-gradient centrifugations. In the peroxisomal fractions, the activity of the photorespiration, beta-oxidation and glyoxylate cycle enzymes, and the ROS-related enzymes catalase, superoxide dismutase, xanthine oxidase, glutathione reductase and NADP(+)-dehydrogenases, was determined. Most enzymes studied had higher specific activity and protein content in green than in red fruits. By native PAGE and western blot analysis, the localisation of a Mn-SOD in fruit peroxisomes was demonstrated. The ascorbate and glutathione levels were also determined in crude extracts and in peroxisomes purified from both green and red peppers. The total ascorbate content (200-220 mg per 100 g FW) was similar in crude extracts from the two types of fruits, but higher in peroxisomes from red peppers. The glutathione concentration was 2-fold greater in green pepper crude extracts than in red fruits, whereas peroxisomes from both tissues showed similar values. The presence in pepper peroxisomes of different antioxidative enzymes and their corresponding metabolites implies that these organelles might be an important pool of antioxidants in fruit cells, where these enzymes could also act as modulators of signal molecules (O2*-, H202) during fruit maturation.
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PMID:Peroxisomes from pepper fruits (Capsicum annuum L.): purification, characterisation and antioxidant activity. 1471 45

Capacitation is part of an oxidative process necessary for bovine spermatozoa to acquire fertilizing capacity. This process includes the generation of reactive oxygen species (ROS) and the participation of protein kinases such as A (PKA), C (PKC) and tyrosine kinase (PTK). A redox status is required to support both sperm motility and capacitation. Our aim was to determine the requirement of lactate dehydrogenase C4 (LDH-C4) and isocitrate dehydrogenase (NADP-ICDH) and of protein kinases in cryopreserved bovine sperm capacitation. The presence of inhibitors of both LDH-C4 and NADP-ICDH prevented the heparin-induced capacitation. H89, GF109203X or genistein blocked capacitation triggered by heparin or the superoxide (O(-*)(2))generator system xanthine-xanthine oxidase-catalase (XXOC) suggesting the requirement of PKA, PKC and PTK in this process. Taken together these results suggest that LDH-C4 and NADP-ICDH contribute with the redox status to support bovine sperm capacitation and that PKA, PKC and PTK are involved in different mechanisms induced by different inducers that lead bovine spermatozoa to be capacitated.
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PMID:Heparin- and superoxide anion-dependent capacitation of cryopreserved bovine spermatozoa: requirement of dehydrogenases and protein kinases. 1651 8

Vascular aging is characterized by endothelial dysfunction that is primarily attributed to increased superoxide production, the exact source of which remains ambiguous. This study compared the NAD(P)H and xanthine oxidase (XO) systems as sources of superoxide and impaired vascular function in aging. Male Sprague Dawley rats, 4-months-old (young) and 18-months-old (Aging), were used. Systolic blood pressure was higher (36 +/- 3%) in the aging group compared with young rats, and this was accompanied by reduced acetylcholine-induced renal vasodilatation. Urinary excretion of nitrite was lower in the aging rats (P < 0.05), and this was associated with reduced nitric oxide synthase (NOS) activity and reduced eNOS and iNOS protein expression in the aorta. Aged rats showed a n approximately twofold increase in free radical generation, as evident by increased plasma 8-isoprostane level, and an approximately fourfold increase in proteinuria compared with the young rats. Vascular NADP(H) oxidase was unchanged between both groups, as was the expression of p67phox or p47phox components of NAD(P)H oxidase. However, XO activity was increased (19 +/- 1%; P < 0.05) as well as XO expression in the aorta of aging rats. These results suggest that increased free radical generation-associated increase in SBP in aging rats is XO but not NAD(P)H oxidase-dependent.
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PMID:Oxidative stress-associated vascular aging is xanthine oxidase-dependent but not NAD(P)H oxidase-dependent. 1703 Dec 61


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