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Related Experiment Videos

Evidence for two ethanol oxidizing pathways in reconstituted mixed-function oxidase systems.

G W Winston, A I Cederbaum

    Pharmacology, Biochemistry, and Behavior
    |January 1, 1983
    PubMed
    Summary

    NADPH-cytochrome P-450 reductase oxidizes ethanol and scavengers via a hydroxyl radical pathway. Cytochrome P-450 creates a second, independent ethanol oxidation pathway, suggesting dual mechanisms in microsomal ethanol metabolism.

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    Chemical research in toxicology·2001

    Area of Science:

    • Biochemistry
    • Enzymology
    • Drug Metabolism

    Background:

    • NADPH-cytochrome P-450 reductase and cytochrome P-450 are key enzymes in drug and xenobiotic metabolism.
    • Ethanol metabolism is crucial for understanding alcohol's effects and toxicity.
    • Hydroxyl radicals are highly reactive species implicated in oxidative stress and cellular damage.

    Purpose of the Study:

    • To investigate the mechanisms of ethanol and hydroxyl radical scavenger oxidation by NADPH-cytochrome P-450 reductase and cytochrome P-450.
    • To elucidate the roles of these enzymes and potential radical involvement in ethanol metabolism.
    • To differentiate between reductase-dependent and P-450-mediated ethanol oxidation pathways.

    Main Methods:

    • Purification of NADPH-cytochrome P-450 reductase and cytochrome P-450 from phenobarbital-treated rat liver microsomes.

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  • Enzymatic assays measuring the oxidation rates of ethanol and hydroxyl radical scavengers.
  • Inhibition studies using superoxide dismutase, competing scavengers, desferrioxamine, EDTA, and iron.
  • Assessment of cytochrome P-450's effect on ethanol and scavenger oxidation, including studies with organic hydroperoxides.

    • Main Results:

    • NADPH-cytochrome P-450 reductase alone could oxidize both ethanol and hydroxyl radical scavengers.
    • Reductase-mediated oxidation was sensitive to inhibitors and activators suggesting an iron-catalyzed Haber-Weiss reaction.
    • Cytochrome P-450 addition enhanced ethanol oxidation 2-3 fold, independent of radical scavengers or superoxide dismutase.
    • Ethanol oxidation by the reductase-P450 system was supported by organic hydroperoxides, unlike scavenger oxidation.

    Conclusions:

    • Two distinct pathways contribute to NADPH-dependent microsomal ethanol oxidation.
    • One pathway involves hydroxyl radicals generated by the reductase.
    • A second, independent pathway requires both reductase and cytochrome P-450 and is not oxygen radical-dependent.