Production of superoxide radicals and hydrogen peroxide by NADH-ubiquinone reductase and ubiquinol-cytochrome c reductase from beef-heart mitochondria

Complex I and Complex III supplemented with NADH generated O2− at maximum rates of 9.8 and 6.5 nmol/min/mg of protein, respectively, while, in the presence of superoxide dismutase, the same systems generated H2O2 at maximum rates of 5.1 and 4.2 nmol/min/mg of protein, respectively

Enrique Cadenas

2005

Scholarcy highlights

  • Complex I and Complex III supplemented with NADH generated O2− at maximum rates of 9.8 and 6.5 nmol/min/mg of protein, respectively, while, in the presence of superoxide dismutase, the same systems generated H2O2 at maximum rates of 5.1 and 4.2 nmol/min/mg of protein, respectively
  • H2O2 was essentially produced by disproportionation of O2−, which constitutes the precursor of H2O2
  • A reduced form of ubiquinone appeared to be responsible for the reduction of O2 to O2−, since ubiquinone constituted the sole common major component of Complexes I and III, H2O2 generation by Complex I was inhibited by rotenone, and supplementation of Complex I with exogenous ubiquinones increased the rate of H2O2 generation
  • The efficiency of added quinones as peroxide generators decreased in the order Q1 > Q0 > Q2 > Q6 = Q10, in agreement with the quinone capacity of acting as electron acceptor for Complex I
  • The exogenous quinone was reduced by Complex I and oxidized nonenzymatically by molecular oxygen
  • Additional evidence for the role of ubiquinone as peroxide generator is provided by the generation of O2− and H2O2 during autoxidation of quinols
  • Permanent address: Department of Physiology and Biochemistry, The University of Southampton, Southampton S09 3TU, England

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