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)

Low-potential electron acceptors of photosystem I of chloroplast lamellae produce superoxide anions (0-2) and hydrogen peroxide by autoxidation, but have no effect on ethylene formation from methionine; equimolar amounts of ferredoxin are less active in photosynthetic O-2 and H2O2 production but strongly stimulate ethylene production from methionine. 2. Ten to fifty units of superoxide dismutase inhibit fifty to two hundred units of superoxide dismutase stimulate ethylene formation from methionine by chloroplast lamellae in the presence of ferredoxin. This stimulation is stronger at pH 7.0 than at pH 7.8. Catalase inhibits ethylene formation from methionine. 3. Pulse-radiolytic production of nitrite (NO-2) from hydroxylamine, initiated by hydroxyl radicals (.OH) or O-2, shows no difference in the presence or absence of ferredoxin, nor do the decay kinetics of O2. 4. From the above observations and from model reactions (xanthine/xanthine oxidase; iron salts in the presence of H2O2), it is concluded that reduced ferredoxin in the presence of H2O2 forms a Fenton-type oxidizing species for methionine, generating ethylene in the presence of pyridoxal phosphate. 5. Inhibitory effects of both superoxide dismutase and catalase in oxygen-dependent reactions need not necessarily indicate the participation of the 'Haber-Weiss' reaction.
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PMID:Oxygen activation in isolated chloroplasts. Mechanism of ferredoxin-dependent ethylene formation from methionine. 21 71

Multiple sclerosis (MS) has a much higher incidence among caucasians that in any other race. Furthermore: females are much more susceptible than males and white females living in colder, wetter areas are much more susceptible than those living in warmer areas. On the other hand, menstruating women have increased copper (Cu) absorption and half-life, so they tend to accumulate more Cu than males. Moreover, rapidly growing girls have an increased demand for zinc (Zn), but their rapidly decreasing production of melatonin results in impaired Zn absorption, which is exacerbated by the high Cu levels. The low Zn levels result in deficient CuZnSuperoxide dismutase (CuZnSOD), which in turn leads to increased levels of superoxide. Menstruating females also often present with low magnesium (Mg) and vitamin B6 levels. Vitamin B6 moderates intracellular nitric oxide (NO) production and extracellular Mg is required for NO release from the cell, so that a deficiency of these nutrients results in increased NO production in the cell and reduced release from the cell. The trapped NO combines with superoxide to form peroxinitrite, an extremely powerful free radical that leads to the myelin damage of MS. Iron (Fe), molybdenum (Mo) and cadmium (Cd) accumulation also increase superoxide production. Which explains MS in males, who tend to accumulate Fe much faster and Cu much less rapidly than females. Since vitamin D is paramount for Mg absorption, the much reduced exposure to sunlight in the higher latitudes may account for the higher incidence in these areas. Moreover, vitamin B2 is a cofactor for xanthine oxidase, and its deficiency exacerbates the low levels of uric acid caused by high Cu levels, resulting in myelin degeneration. Finally Selenium (Se) and vitamin E prevent lipid peroxidation and EPA and DHA upregulate CuZnSOD. Therefore, supplementation with 100 mg MG, 25 mg vit B6, 10 mg vit B2, 15 mg Zn and 400 IU vit D and E, 100 microg Se, 180 mg EPA and 120 mg DHA per day between 14 and 16 years of age may prevent MS.
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PMID:The possible role of gradual accumulation of copper, cadmium, lead and iron and gradual depletion of zinc, magnesium, selenium, vitamins B2, B6, D, and E and essential fatty acids in multiple sclerosis. 1098 16

The molybdopterin cofactor (MoCF) is required for the activity of a variety of oxidoreductases. The xanthine oxidase class of molybdoenzymes requires the MoCF to have a terminal, cyanolysable sulphur ligand. In the sulphite oxidase/nitrate reductase class, an oxygen is present in the same position. Mutations in both the ma-l gene of Drosophila melanogaster and the hxB gene of Aspergillus nidulans result in loss of activities of all molybdoenzymes that necessitate a cyanolysable sulphur in the active centre. The ma-l and hxB genes encode highly similar proteins containing domains common to pyridoxal phosphate-dependent cysteine transulphurases, including the cofactor binding site and a conserved cysteine, which is the putative sulphur donor. Key similarities were found with NifS, the enzyme involved in the generation of the iron-sulphur centres in nitrogenase. These similarities suggest an analogous mechanism for the generation of the terminal molybdenum-bound sulphur ligand. We have identified putative homologues of these genes in a variety of organisms, including humans. The human homologue is located in chromosome 18.q12.
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PMID:Comparison of the sequences of the Aspergillus nidulans hxB and Drosophila melanogaster ma-l genes with nifS from Azotobacter vinelandii suggests a mechanism for the insertion of the terminal sulphur atom in the molybdopterin cofactor. 1102 94

The xanthine oxidase class of molybdenum enzyzmes requires a terminal sulfur ligand at the active site. It has been proposed that a special sulfurase catalyzes the insertion of this ligand thereby activating the enzymes. Previous analyses of mutants in plants indicated that the genetic locus aba3 is involved in this step leading to activation of the molybdenum enzymes aldehyde oxidase and xanthine dehydrogenase. Here we report the cloning of the aba3 gene from Arabidopsis thaliana and the biochemical characterization of the purified protein. ABA3 is a two-domain protein with a N-terminal NifS-like sulfurase domain and a C-terminal domain that might be involved in recognizing the target enzymes. Molecular analysis of three aba3 mutants identified mutations in both domains. ABA3 contains highly conserved binding motifs for pyridoxal phosphate and for a persulfide. The purified recombinant protein possesses a cysteine desulfurase activity, is yellow in color, and shows a NifS-like change in absorbance in the presence of L-cysteine. Pretreatment of ABA3 with a thiol-specific alkylating reagent inhibited its desulfurase activity. These data indicate a transsulfuration reaction similar to bacterial NifS. In a fully defined in vitro system, the purified protein was able to activate aldehyde oxidase by using L-cysteine as sulfur donor. Finally, we show that the expression of the aba3 gene is inducible by drought-stress.
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PMID:ABA3 is a molybdenum cofactor sulfurase required for activation of aldehyde oxidase and xanthine dehydrogenase in Arabidopsis thaliana. 1155 8

The transition element molybdenum (Mo) is of essential importance for (nearly) all biological systems as it is required by enzymes catalyzing diverse key reactions in the global carbon, sulfur and nitrogen metabolism. The metal itself is biologically inactive unless it is complexed by a special cofactor. With the exception of bacterial nitrogenase, where Mo is a constituent of the FeMo-cofactor, Mo is bound to a pterin, thus forming the molybdenum cofactor (Moco) which is the active compound at the catalytic site of all other Mo-enzymes. In eukaryotes, the most prominent Mo-enzymes are (1) sulfite oxidase, which catalyzes the final step in the degradation of sulfur-containing amino acids and is involved in detoxifying excess sulfite, (2) xanthine dehydrogenase, which is involved in purine catabolism and reactive oxygen production, (3) aldehyde oxidase, which oxidizes a variety of aldehydes and is essential for the biosynthesis of the phytohormone abscisic acid, and in autotrophic organisms also (4) nitrate reductase, which catalyzes the key step in inorganic nitrogen assimilation. All Mo-enzymes, except plant sulfite oxidase, need at least one more redox active center, many of them involving iron in electron transfer. The biosynthesis of Moco involves the complex interaction of six proteins and is a process of four steps, which also includes iron as well as copper in an indispensable way. Moco as released after synthesis is likely to be distributed to the apoproteins of Mo-enzymes by putative Moco-carrier proteins. Xanthine dehydrogenase and aldehyde oxidase, but not sulfite oxidase and nitrate reductase, require the post-translational sulfuration of their Mo-site for becoming active. This final maturation step is catalyzed by a Moco-sulfurase enzyme, which mobilizes sulfur from l-cysteine in a pyridoxal phosphate-dependent manner as typical for cysteine desulfurases.
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PMID:Cell biology of molybdenum. 1678 86