Mitochondrial superoxide anion production and release into intermembrane space.

The topological distribution of ubiquinone in the mitochondrial respiratory chain suggests that both ubiquinone pools may participate in O2.- production and, hence, are vectorially released into the matrix and intermembrane space. Mitoplasts, obtained by either digitonin or hypotonic KCl treatment, are a suitable experimental model for measuring O2.- in the intermembrane space. The use of membrane-impermeable spin-broadening agents strengthens the notion that part of the O2.- generated by the respiratory chain may be released into the intermembrane space. This, together with the putative occurrence of a Cu, Zn-superoxide dismutase in this compartment may account for part of H2O2 released by mitochondria and contributing to a cytosolic steady-state level of this species in cytosol.