Evidence for an ATP-driven "proton pump" in rat liver lysosomes by basic dyes uptake.

When rat liver lysosomes are suspended in a medium containing acridine orange at neutral pH, accumulation of the dye may be observed within the vesicles. The uptake appears driven by a pH gradient between the external medium and the interior of the lysosomes since it is inhibited by NH₄⁺, nigericin and other electroneutral proton-cation exchangers. FCCP is ineffective in inhibiting the uptake. In the presence of Mg⁺⁺ and anions such as Cl^?, ATP promoted a further and more extensive but slower oligomycin and ouabain-insensitive dye uptake, which was also inhibited by FCCP. Very similar results were obtained with neutral red and atebrin. When the rate of the ATP-induced acridine uptake in preparations of different purification grade was compared, it was observed that the uptake rate increased in parallel with lysosomal enzymatic activity. These results suggest that an electrogenic ATP-driven-Mg⁺⁺ dependent “proton pump” is operating in the lysosomal membrane, as previously proposed.