Preincubation of the vesicles with nitrate caused inhibition of proton pumping and ATPase activity, with similar concentration dependence. Fluoride, which preferentially inhibits the plasma membrane ATPase, inhibited ATPase activity strongly at concentrations which did not affect proton pumping activity.

Addition of potassium salts, after a steady-state pH gradient is established in the absence of such salts, caused an increased pH gradient which was due to alleviation of Δ Ψ and subsequent increased influx of H⁺ into these vesicles. This anion-induced increase in the pH gradient could be used as a measure of the relative anion permeabilities, which were of the order Br⁻ = NO₃⁻ > Cl⁻ SO₄²⁻. Phosphate and fluoride caused no increase in the pH gradient. Since the concentration dependence of KCl- and KNO₃-induced quenching exhibited a saturable component, and since H⁺ uptake was increased by only certain anions, the data suggest that there may be a relatively specific anion channel associated with tonoplast-derived vesicles.