Evidence for a vacuolar-type proton ATPase in Entamoeba histolytica.

Entamoeba histolytica is a primitive eukaryote that lacks mitochondria. Golgi and a well-developed endoplasmic reticulum. Close to half of the cell volume is occupied by pinocytic vesicles, which are in continuous turnover with the plasma membrane and perform functions that in higher eukaryotic cells are taken over by lysosomes. Similar to the latter, the amebal vesicles are acidified. We report here that bafilomycin A1, a specific inhibitor of vacuolar-type (V-) ATPases, suppressed this acidification at submicromolar concentrations; concomitantly, it inhibited pinocytosis. These results strongly suggest the presence of a V-ATPase in pinocytic vesicles of E. histolytica, and thereby support the notion that the V-ATPases in the organelles of higher eukaryotes are derived from an archaic plasma membrane-bound form.