Inhibition of mitocondrial complex III by nitric oxide.

IGLESIAS DE; BOMBICINO SS; BOVERIS A,; VALDEZ LB

Puerto Madryn

Congreso; 46th Annual Meeting Argentine Society for Biochemistry and Molecular Biology -XLVI Reunión Annual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2010

Sociedad Argentina de Bioquimica y Biologia Molecular

NO is a physiological regulator of mitochondrial function: NO inhibits cytochrome oxidase activity competitively with O2 and electron transfer between cyt. b and c. Little is known about how NO interacts with the NO-reactive component of the ubiquinone-cyt. b area of the mitochondrial respiratory chain. The aim of this work was to study the NO inhibitory effect on electron transfer between cyt. b and c. Succinate-cytochrome c reductase activity, and H2O2 and O2- production rates were measured using beef heart submitochondrial particles and S-nitrosoglutathione (GSNO; 0-750 uM) as NO donor. NO inhibited succinate-cytochrome c reductase activity with a maximal effect (55%) at 500 uM GSNO (6 microM NO) being this inhibition independent on [O2]. The effect of NO on respiration chain produced a hyperbolic increase in O2- and H2O2 production with a maximal rate at 500 microM GSNO (1.1 +/- 0.2nmolO2-/min.mgprotein; 0.55+- 0.05nmolH2O2/min.mgprotein). The ratio O2-/H2O2 was 2.0 in accordance to the stoichiometry of the O2- dismutation reaction. At 150 microM GSNO (2 microM NO) succinate-cytochrome c reductase activity was inhibited by 33% while O2- and H2O2 productions were increased by 36% and 31%, respectively. These preliminary results show that the interaction of NO with complex III leads to the inhibition of mitochondrial electron transfer and an enhancement of O2- production by ubisemiquinone autooxidation.