Ecto-nucleotide triphosphatase activity in pathogenic and non-pathogenic Entamoeba: protection from the cytotoxic effects of extracellular ATP.

The nucleotide triphosphatase (NTPase) activity of Entamoeba species and of Entamoeba histolytica strains, was compared. In all cases, with the exception of Entamoeba moshkovskii, the enzyme was activated by Ca2+ and not by Mg2+ and preferentially hydrolysed UTP with decreasing activity for ATP and GTP. The NTPase activity was associated with both the intracellular and the plasma membrane sulphonylbenzoyl-adenosine (FSBA) of trophozoites in which the ATP-site was facing externally, as shown by fluoroinhibition of NTPase activity and protection by the substrate added prior to FSBA. The highest surface activity was found in Entamoeba invadens and in the virulent E. histolytica HM1-A clone (HM1-IMSS passaged thrice through hamster liver). Significant lower activity was observed in non-pathogenic Entamoeba spp. The addition of ATP to cultures of pathogenic amoebae resulted in cell growth inhibition and lysis. This deleterious effect of adding ATP to the cultures was reversed by the addition of Ca2+. ATP hydrolysis by the amoeba may alter extracellular ATP-dependent processes in the host, which may be important for the survival of the amoeba in vivo.