Membrane bound pyrophosphatases in Entamoeba histolytica.

Entamoeba histolytica homogenates are capable of hydrolyzing a range of inorganic and organic pyrophosphates. Two separate activities are present: an inorganic pyrophosphatase hydrolyzing inorganic pyrophosphate and linear tripolyphosphate, and a nucleoside diphosphatase hydrolyzing thiamine pyrophosphate and nucleoside diphosphates (ADP, GDP and UDP). The inorganic pyrophosphatase has an acid pH optimum, a relatively high KM (congurent to 1 micrometer) and is markedly heat stable and lacks a metal requirement. The nucleoside diphosphatase also has an acid pH optimum but displays a much higher affinity for substrate (KM congurent to 50 micrometer), is unstable to heating and is activated by Ca ions. Both pyrophosphatases distinct from the acid phosphatase activity which is also present. All three hydrolases are sedimentable and latent suggesting their association with membrane bounded organelles. No soluble inorganic pyrophosphatase activity could be demonstrated.