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)

A molybdenum cofactor (Mo-co) from xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) can be isolated from the enzyme by a technique that has been used to isolate an iron-molybdenum cofactor (FeMo-co) from component I of nitrogenase. N-Methylformamide is used for the extraction of these molybdenum cofactors. Mo-co from xanthine oxidase activates nitrate reductase (NADPH:nitrate oxidoreductase, EC 1.6.6.2) in an extract from Neurospora crassa mutant strain Nit-1; however, FeMo-co is unable to activate nitrate reductase in strain Nit-1. Mo-co from xanthine oxidase is unable to activate nitrogenase in an extract of Azotobacter vinelandii mutant strain UW45. Inactive component I in this extract can be activated by FeMo-co. These results indicate that nitrate reductase and xanthine oxidase share a common molybdenum cofactor, but this cofactor is different from the molybdenum cofactor in nitrogenase.A. vinelandii synthesizes both Mo-co and FeMo-co. Mo-co is produced when the cells fix N(2) and also when they are repressed for nitrogenase synthesis by growth in a medium containing excess ammonium. However, FeMo-co is not produced when cells are grown in an ammonium-containing medium. Partially purified preparations of component I from A. vinelandii and Klebsiella pneumoniae contain both FeMo-co and Mo-co. The presence of both FeMo-co and Mo-co activities in partially purified preparations of component I explains previous reports of activation of inactive nitrate reductase in strain Nit-1 by acid-treated component I of nitrogenase. The Mo-co can be separated from FeMo-co in these preparations by chromatography on Sephadex G-100 in N-methylformamide. Both FeMo-co and Mo-co are sensitive to oxygen.
 ...
PMID:Molybdenum cofactors from molybdoenzymes and in vitro reconstitution of nitrogenase and nitrate reductase. 14 98

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

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.
 ...
PMID:Purification and partial characterization of caffeine oxidase--A novel enzyme from a mixed culture consortium. 1049 16

Catabolism of caffeine (1,3,7-trimethylxanthine) in microorganisms commences via two possible mechanisms: demethylation and oxidation. Through the demethylation route, the major metabolite formed in fungi is theophylline (1,3-dimethylxanthine), whereas theobromine (3,7-dimethylxanthine) is the major metabolite in bacteria. In certain bacterial species, caffeine has also been oxidized directly to trimethyl uric acid in a single step. The conversion of caffeine to its metabolites is primarily brought about by N-demethylases (such as caffeine demethylase, theobromine demethylase and heteroxanthinedemethylase), caffeine oxidase and xanthine oxidase that are produced by several caffeine-degrading bacterial species such as Pseudomonas putida and species within the genera Alcaligenes, Rhodococcus and Klebsiella. Development of biodecaffeination techniques using these enzymes or using whole cells offers an attractive alternative to the present existing chemical and physical methods removal of caffeine, which are costly, toxic and non-specific to caffeine. This review mainly focuses on the biochemistry of microbial caffeine degradation, presenting recent advances and the potential biotechnological application of caffeine-degrading enzymes.
 ...
PMID:Catabolic pathways and biotechnological applications of microbial caffeine degradation. 1700 88