Open Access

ARTICLE

Superoxide and hydrogen peroxide productions by NO-inhibited complex III

Darío E. IGLESIAS^*, Silvina S. BOMBICINO, Alberto BOVERIS, Laura B. VALDEZ

* Address correspondence to: Darío E. Iglesias, diglesias@ffyb.uba.ar

BIOCELL 2016, 40(1), 27-30. https://doi.org/10.32604/biocell.2016.40.027

Abstract

Complex III plays a central role in the mitochondrial respiratory chain transferring electrons from ubiquinol to cytochrome c and pumping protons to the intermembrane space, contributing to the protonmotive force. Furthermore, complex III can act as a source of O₂ •- in the presence of ubiquinol and antimycin, an expermiental condition in which the oxidation of the cytochrome b hemes is blocked. The O₂ •- dismutation catalyzed by superoxide dismutase produces H₂O₂, a known second messenger in redox signalling. Results from our laboratory have shown that NO, released from GSNO or from SPER -NO or generated by mtNOS, inhibits electron transfer at ubiquinone-cytochrome b area producing antimycin-like effects. Thus, both antimycin- and NO-inhibited complex III showed a high content of cytochromes b in the reduced state (79 and 71%, respectively) and an enhancement in the ubisemiquinone EPR signal at g=1.99 (42 and 35%, respectively). As consequence, O₂ •- and H₂O₂ productions were increased, being the O₂ •-/H₂O₂ ratio equal to 1.98 in accordance with the stoichiometry of the O₂ •- disproportionation. The interruption of the oxidation of cytochromes b by NO leads to an enhancement of the steady-state concentration of UQH• , allowing cytochrome bc₁ complex to act as a source of reactive oxygen species in physiological conditions.

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