The acidification of rat liver lysosomes in vitro: a role for the membranous ATPase as a proton pump.

Lysosomes were purified from the livers of rats which had been treated with Triton WR-1339. The ATPase activity of these lysosomes was stimulated by preincubation with NaCl or KCl, conditions which diminish the proton gradient due to Donnan equilibrium. Subsequent to this preincubation measurements of methylamine uptake by lysosomes showed an ATP-dependent enhancement. Simultaneous measurements of the internal volumes of lysosomes confirmed that ATP-dependent methylamine uptake is due to acidification of lysosomes by 0.3 to 0.5 pH units. Because the conditions which stimulated ATP-dependent methylamine uptake also stimulated the ATPase activity it is concluded that acidification of lysosomes requires an ATPase which functions as a proton pump.