Modulation of the electrophoretic ATP‐induced K ‐transport in yeast mitochondria by ΔpH

The modulation of the ATP‐induced K+‐transport pathway of the yeast inner mitochondrial membrane by ΔpH was investigated in two ways. First, the inhibitory effect of phosphate was compared to the effect of other permeant acids, demonstrating that a part of the effect of phosphate was linked to its electroneutral transport down ΔpH. However, an additional effect specific for phosphate also occured inside the matrix. Second, the stimulation of the respiration by ATP in the presence of K+ was compared to the effects of the protonophore C1CCP2 and of the K+‐ionophore valinomycin. Quite unexpectedly, the effect of ATP looked more like the effect of CICCP than the effect of valinomycin. This and previous results (Manon et al., Biochimica et Biophysica Acta 1231, 282‐288 (1995)) show that the rate of electrophoretic K+‐entry is limited by the rate of electroneutral K+‐exit via the K+/H+ exchange and is therefore ΔpH‐dependent.