Entamoeba histolytica: Ouabain-insensitive Na+-ATPase activity

Our aim was to determine the presence of sodium pumps in Entamoeba histolytica. It is shown through the measurement of ouabain-sensitive ATPase activity and immunoblotting that E. histolytica does not express (Na++K+)ATPase. On the other hand, we observed a Na+-ATPase with the following characteristics: (1) stimulated by Na+ or K+, but these effects are not addictive; (2) the apparent affinity is similar for Na+ and K+ (K0.5 = 13.3 ± 3.7 and 15.4 ± 3.1 mM, respectively), as well as the Vmax (24.9 ± 1.5 or 27.5 ± 1.6 nmol Pi mg−1 min−1, respectively); (3) insensitive up to 2 mM ouabain; and (4) inhibited by furosemide with an IC50 of 0.12 ± 0.004 mM. Furthermore, this enzyme forms a Na+- or K+-stimulated, furosemide- and hydroxylamine-sensitive ATP-driven acylphosphate phosphorylated intermediate.