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Related Experiment Videos

Superoxide anion generation by the cytochrome bc1 complex.

Jian Sun1, Bernard L Trumpower

  • 1Department of Biochemistry, Dartmouth Medical School, 7200 Vail, Hanover, NH 03755, USA.

Archives of Biochemistry and Biophysics
|November 1, 2003
PubMed
Summary

Superoxide anion generation by cytochrome bc1 complexes is similar in yeast and mammals. Inhibitor binding and enzyme activity, not redox potential changes, primarily influence superoxide production rates.

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Area of Science:

  • Biochemistry
  • Mitochondrial Respiration
  • Reactive Oxygen Species

Background:

  • Cytochrome bc1 complexes are crucial for cellular respiration.
  • Superoxide anion generation is a byproduct of mitochondrial electron transport.
  • Understanding superoxide production mechanisms is vital for studying oxidative stress.

Purpose of the Study:

  • To investigate superoxide anion generation in isolated cytochrome bc1 complexes from bovine and yeast mitochondria.
  • To examine the impact of specific inhibitors and mutations on superoxide production rates.
  • To elucidate the role of redox component midpoint potentials in superoxide formation.

Main Methods:

  • Isolation of cytochrome bc1 complexes from bovine heart and yeast mitochondria.
  • Utilizing yeast mutants with altered cytochrome b heme and Rieske iron-sulfur cluster midpoint potentials.

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  • Measuring superoxide anion generation rates in the presence and absence of inhibitors (stigmatellin, myxothiazol, antimycin).
  • Assessing cytochrome c reduction and reductase activity.

    • Main Results:

    • Superoxide anion production ranged from 3-5% of cytochrome c reduction rate, highest without inhibitors.
    • Stigmatellin abolished superoxide formation; myxothiazol and antimycin allowed low-rate production.
    • Altering cytochrome b heme midpoint potentials had minimal effect on superoxide generation.
    • A mutation lowering the Rieske iron-sulfur cluster potential reduced superoxide formation and reductase activity.

    Conclusions:

    • Superoxide anion is generated by similar mechanisms in mammalian and yeast cytochrome bc1 complexes.
    • Enzyme activity, influenced by inhibitor binding and functional redox components, is key to superoxide formation.
    • Redox component midpoint potential changes have minor effects on superoxide generation unless enzyme activity is significantly impacted.