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)

1. Pteridin-4-ones, methylated at nitrogen or carbon, N-methylated lumazines and related oxopteridines were studied as substrates of a highly purified bovine milk xanthine oxidase (xanthine : oxygen oxidoreductase, EC 1.2.3.2). 2. The enzyme can oxidise at high rates both uncharged and anionic substrates. Variation of enzymic activity with pH is mainly due to pH-dependent changes in the active enzymic center. 3. Milk xanthine oxidases at different stages of purification convert pteridin-4-one into the 4,7-dione (compound 13 in this article). 4. Methylation at C-6 in the pyrazine moiety enhances enzymic attack at C-2 in the pyrimidine ring. N-Methylation may increase or reduce rates of oxidation. 5. For oxidation at C-2, the most favorable form of the substrate bears a double bond at C(2) = N(3). Attack at C-7 is enhanced strongly in structures bearing a double bond at C(6) = C(7). 6. In general, pteridines react with xanthine oxidase as non-hydrated molecules. However, oxidation of 8-methyllumazine at C-7 may take place by dehydrogenation of the 7-CHOH group of the covalently hydrated molecule.
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PMID:Oxidation of methyl derivatives of pteridin-4-one, lumazine and related pteridines by bovine milk xanthine oxidase. 1 25

Cypridina luciferin analogs have been widely used as a specific chemiluminescence probe for the detection of superoxide anion (O2-) and singlet oxygen (1O2). However, light emission during the reaction of Cypridina luciferin analogs and other active oxygen species (AOS) has not been reported in detail. Therefore, we re-evaluated 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazine-3-one (MCLA), one of the Cypridina luciferin analogs, as a chemiluminescence probe to detect various AOS. MCLA-dependent chemiluminescence was observed when MCLA was incubated with the following systems; 1) hypoxanthine plus xanthine oxidase (O2-), 2) thermolysis of endoperoxide (1O2), 3) hydrogen peroxide plus ferrous ion (hydroxyl radical), 4) ferrous ion, 5) thermolysis of azo compound (alkyl peroxyl radical) and 6) hydrogen peroxide. Superoxide dismutase inhibited MCLA-dependent chemiluminescence observed during ferrous ion-induced decomposition of hydrogen peroxide. Alkyl peroxyl radical reacted with MCLA, but light was not emitted when the concentration of MCLA was high. These results suggest that radicals, except O2-, appeared not to be direct inducers of MCLA-dependent light emission. In summary, MCLA-dependent chemiluminescence was induced by various AOS in addition to O2- and 1O2, but active species must be O2- and 1O2 in many cases. These points should be appreciated when Cypridina luciferin analogs, such as MCLA, are used for the detection of AOS.
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PMID:Reestimation of Cypridina luciferin analogs (MCLA) as a chemiluminescence probe to detect active oxygen species--cautionary note for use of MCLA. 1297 6

The probe 3,7-dihydro-2-methyl-6-(4-methoxyphenyl)imidazol[1,2-a]pyrazine-3-one (MCLA) is widely used for studying the superoxide anion production and the efficiency of antioxidants in biological systems. Here we report that a number of sulfur-containing compounds applied in biochemical and cytological studies are able to suppress MCLA-derived chemiluminescence (MDCL) independent of their capability to scavenge superoxide anion. The most effective MDCL quenchers appeared to be the substances with thiocarbamoyl and thiocarbonyl groups coupled to cyclic molecules and several thiol- and disulfide-containing compounds. The analysis of MDCL kinetics in a xanthine oxidase system allows one to rapidly discriminate between true antioxidants and the quenchers of chemiluminescence.
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PMID:Sulfur-containing compounds quench 3,7-dihydro-2-methyl-6-(4-methoxyphenyl)imidazol[1,2-a]pyrazine-3-one chemiluminescence: Discrimination between true antioxidants and quenchers using xanthine oxidase. 2061 82