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Related Experiment Videos

Exclusive CO binding to cytochrome oxidase.

Y Orii

    Journal of Inorganic Biochemistry
    |March 1, 1985
    PubMed
    Summary

    Carbon monoxide (CO) binding to cytochrome oxidase traps the unliganded reduced heme a3. Inhibitory ligands like azide, cyanide, or fluoride did not significantly alter CO compound reactions, suggesting CO is the primary ligand near the heme a3-CuB center.

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    Area of Science:

    • Biochemistry
    • Enzyme kinetics
    • Bioenergetics

    Background:

    • Cytochrome oxidase is a crucial enzyme in cellular respiration.
    • Understanding ligand interactions at the heme a3-CuB center is key to its function.
    • Previous studies have investigated various inhibitors of cytochrome oxidase.

    Purpose of the Study:

    • To investigate the binding and behavior of carbon monoxide (CO) with cytochrome oxidase.
    • To determine the role of inhibitory ligands (azide, cyanide, fluoride) in CO compound formation and subsequent reactions.
    • To elucidate the structural and dynamic state of the heme a3-CuB center during CO interaction.

    Main Methods:

    • Spectroscopic analysis of cytochrome oxidase treated with inhibitory ligands and then CO.
    • Flow-flash experiments to study reactions with dioxygen.
    • Kinetic measurements of ligand photodissociation and reassociation.

    Main Results:

    • CO addition to reduced cytochrome oxidase, pretreated with azide, cyanide, or fluoride, resulted in CO-ferrous heme a3 trapping.
    • The dissociation of ligand-bound ferric heme a3 was rate-limiting for CO compound formation in some cases.
    • Pretreatment with inhibitory ligands minimally affected photodissociation, reassociation, and reaction with dioxygen, except for a slight decrease in electron transfer rate with cyanide.
    • These findings indicate that only CO, not the inhibitory ligands, remains near the heme a3-CuB center in the CO compound.

    Conclusions:

    • The heme a3-CuB center in cytochrome oxidase readily traps CO in its reduced, unliganded state.
    • Inhibitory ligands do not significantly impede the formation or subsequent reactivity of the CO compound.
    • The results strongly suggest that CO is the predominant ligand in the vicinity of the heme a3-CuB center within the CO-cytochrome oxidase complex.

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