Valinomycin binds stoichiometrically to cytochrome c oxidase and changes its structure and function.

Valinomycin binds to soluble and reconstituted cytochrome c oxidase (COX) in a stoichiometric manner, as shown by a spectral shift of the oxidized gamma-band. No spectral change is found with nigericin or 18-crown-6 and in the absence of potassium ions. Titration of the proton pumping activity of reconstituted COX with valinomycin reached a maximum of H+/e- - 0.73 after addition of 1 mole of valinomycin per mole of reconstituted COX. It is concluded that K+-translocation in proton-pumping COX vesicles occurs via enzyme-bound valinomycin.