ENTRY       EC 1.1.3.22
NAME        Xanthine oxidase
            Hypoxanthine oxidase
CLASS       Oxidoreductases
            Acting on the CH-OH group of donors
            With oxygen as acceptor
SYSNAME     Xanthine:oxygen oxidoreductase
REACTION    Xanthine + H2O + O2 = Urate + H2O2
SUBSTRATE   Xanthine
            Hypoxanthine
            Purine
            Pterin
            Aldehyde
            H2O
            O2
PRODUCT     Urate
            H2O2
            O2-
INHIBITOR   Disulfiram
COFACTOR    FAD
            Iron
            Molybdenum
COMMENT     An iron-molybdenum flavoprotein (FAD). Also oxidizes
            hypoxanthine, some other purines and pterins, and aldehydes
            (i.e. possesses the activity of EC 1.2.3.1);
            probably acts on the hydrated derivatives of these substrates.
            Under some conditions the product is mainly superoxide rather
            than peroxide: R-H + H2O = ROH + 2 O2-.
            The enzyme from animal tissues can be interconverted to EC
            1.1.1.204. That from liver exists in vivo mainly as the
            dehydrogenase form, but can be converted into the oxidase form
            by storage at -20C, by treatment with proteolytic enzymes or
            with organic solvents, or by thiol reagents such as Cu2+,
            N-ethylmaleimide or 4-mercuribenzoate. The effect of
            thiol reagents can be reversed by thiols such as 1,4-
            dithioerythritol. EC 1.1.1.204 can also be converted into EC
            1.1.3.22 by EC 1.8.4.7 in the presence of oxidized glutathione.
            The Micrococcus enzyme can use ferredoxin as acceptor.
            Formerly EC 1.2.3.2.
PATHWAY     PATH: MAP00230  Purine metabolism
DISEASE     MIM: 278300  Xanthine dehydrogenase (xanthine oxidase);
                         Xanthinuria, type I (3)
MOTIF       PS: PS00197  C-{C}-{C}-[GA]-{C}-C-[GAST]-{cpdhtmEKRHFYW}-C
            PS: PS00559  [GA]-x(3)-[KRNQHT]-x(11,14)-[LIVMFYWS]-x(8)-[LIVMF]-x-
                         C-x(2)-[DEN]-R-x(2)-[DE]
DBLINKS     University of Geneva ENZYME DATA BANK: 1.1.3.22
            WIT (What Is There) Metabolic Reconstruction: 1.1.3.22
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