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Cytochrome oxidase: an alternative model.

C H Seiter, S G Angelos

    Proceedings of the National Academy of Sciences of the United States of America
    |April 1, 1980
    PubMed
    Summary
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    Strongly oxidizing conditions reveal a stable Cu(I) center in cytochrome oxidase, suggesting its cytochrome a3 is a two-electron redox center with stable Fe(IV), Fe(III), and Fe(II) states.

    Area of Science:

    • Biochemistry
    • Biophysics
    • Enzyme kinetics

    Background:

    • Cytochrome oxidase (cytochrome c oxidase; ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) is a crucial enzyme in cellular respiration.
    • Understanding its redox properties is key to elucidating electron transfer mechanisms.
    • Previous models often assume antiferromagnetic coupling, which may not fully capture its behavior.

    Purpose of the Study:

    • To investigate the redox states of copper centers in cytochrome oxidase under strongly oxidizing conditions.
    • To propose an alternative model for the cytochrome a3 redox center.

    Main Methods:

    • Oxidative titration of reduced cytochrome oxidase.
    • Electron paramagnetic resonance (EPR) spectroscopy.
    • Potentiometry (potentials > +500 mV vs. neutral hydrogen electrode) in the presence of carbon monoxide and sulfide.

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    Main Results:

    • No new copper signals were observed in the EPR spectrum under strongly oxidizing conditions.
    • This indicates that at least one copper center remains in the Cu(I) state.
    • Spectroscopic data supports a model where cytochrome a3 acts as a two-electron redox center.

    Conclusions:

    • Cytochrome a3 likely functions as a two-electron redox center, accommodating stable Fe(IV), Fe(III), and Fe(II) states.
    • This proposed model offers a rationalization for observed spectroscopic data.
    • The model does not necessitate an antiferromagnetic coupling scheme, contrasting with existing theories.