Entamoeba histolytica : ouabain-insensitive Na+-ATPase activity

Abstract

6 p. : il.Our aim was to determine the presence of sodium pumps in Entamoeba histolytica. It is shown through the measurement of ouabainsensitive 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