Xanthine oxidase catalyzes the synthesis of retinoic acid

Gennaro Taibi, Maria Concetta Gueli

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    Abstract

    Milk xanthine oxidase (xanthine: oxygen oxidoreductase; XO; EC 1.1.3.22) was found to catalyze the conversion of retinaldehyde to retinoic acid. The ability of XO to synthesize all trans-retinoic acid efficiently was assessed by its turnover number of 31.56 min-1, determined at pH 7.0 with 1 nM XO and all trans-retinaldehyde varying between 0.05 to 2 microM. The determination of both retinoid and purine content in milk was also considered in order to correlate their concentrations with kinetic parameters of retinaldehyde oxidase activity. The velocity of the reaction was dependent on the isomeric form of the substrate, the all trans- and 9-cis-forms being the preferred substrates rather than 13-cis-retinaldehyde. The enzyme was able to oxidize retinaldehyde in the presence of oxygen with NAD or without NAD addition. In this latter condition the catalytic efficiency of the enzyme was higher. The synthesis of retinoic acid was inhibited 87% and 54% by 4 microM and 2 microM allopurinol respectively and inhibited 48% by 10 microM xanthine in enzyme assays performed at 2 microM all trans-retinaldehyde. The Ki value determined for xanthine as an inhibitor of retinaldehyde oxidase activity was 4 microM.
    Lingua originaleEnglish
    pagine (da-a)275-285
    Numero di pagine11
    RivistaJournal of Enzyme Inhibition
    Volume16
    Stato di pubblicazionePublished - 2001

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    All Science Journal Classification (ASJC) codes

    • Biochemistry
    • Molecular Medicine

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