On the inhibiting effect of oligomycin on Mg: ATP-dependent ΔpH and Δψ in microsomal vesicles from radish

The kinetics of inhibition by oligomycin of the mitochondrial ATPase and the Mg: ATP-dependent electrogenic transport of protons were compared in membrane preparations from radish seedlings. Oligomycin blocks the phosphohydrolyzing activity of mitochondrial ATPase (measured at pH 8.5) at 1 μg × mg−1 prot and the ATP-synthase one (measured at pH 6.6) at 3 μg × mg−1 prot. Oligomycin at these concentrations does not influence Mg: ATP-dependent proton transport and Mg: ATP-dependent hyperpolarization of transmembrane electric potential difference (PD) in microsomal vesicles. However, an inhibiting effect of the drug becomes apparent at concentrations higher than 10 μg × mg−1 prot, increasing with the increase of oligomycin concentration at least up to 240 μg × mg−1 prot. Both the vanadate and the NO3−-sensitive systems of Mg: ATP-dependent electrogenic transport of protons show similar sensitivity to oligomycin.