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Related Experiment Videos

Mixed-valence cytochrome oxidase-formate complex. A steady-state intermediate.

T Brittain, C Greenwood, A Johnson

    The Biochemical Journal
    |December 1, 1977
    PubMed
    Summary

    Formate binding to cytochrome c oxidase changes its reaction with reducing agents. A mixed-valence species, stable under specific conditions, was characterized using spectroscopy.

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    Area of Science:

    • Biochemistry
    • Biophysics
    • Enzyme kinetics

    Background:

    • Cytochrome c oxidase is a key enzyme in cellular respiration.
    • Formate binding to haem a3 influences enzyme reactivity.
    • Understanding enzyme-redox states is crucial for elucidating electron transfer mechanisms.

    Purpose of the Study:

    • To investigate the reactivity of the formate-cytochrome c oxidase complex with different reducing agents.
    • To characterize the stability and properties of the mixed-valence species formed.
    • To elucidate the redox states of the enzyme components in the mixed-valence complex.

    Main Methods:

    • Enzyme kinetics studies using sodium dithionite and ascorbate/tetramethylenephenylene-diamine as reducing agents.
    • Spectroscopic characterization of the mixed-valence species using electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD).

    Main Results:

    • Formate complex formation alters the reaction pathway with reducing agents compared to the unliganded enzyme.
    • A mixed-valence species is formed under specific reduction conditions (ascorbate/TMPD) and is stable only with excess O2 and reducing equivalents.
    • EPR and MCD spectroscopy revealed the mixed-valence state comprises reduced low-spin haem a, reduced copper, and high-spin ferric haem a3.

    Conclusions:

    • The formate-cytochrome c oxidase complex exhibits distinct reactivity profiles based on the reducing agent used.
    • The mixed-valence species represents a transient but characterizable steady-state intermediate in the enzyme's reaction cycle.
    • Detailed spectroscopic analysis provides insights into the specific redox states of the enzyme's prosthetic groups within this intermediate.

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