Entamoeba histolytica: An ecto-phosphatase activity regulated by oxidation–reduction reactions

In this work, an ecto-phosphatase activity of Entamoeba histolytica was characterized using intact cells. This activity presented the following biochemical characteristics: (i) it hydrolyzes p-NPP with Vmax of 8.00 ± 0.22 nmol p-NP × h−1 × 10−5 cells and Km of 2.68 ± 0.25 mM; (ii) it is inhibited by acid phosphatase inhibitors, such as sodium molybdate (Ki = 1.70 ± 0.24 μM) and sodium fluoride (Ki = 0.25 ± 0.02 mM); (iii) it also showed high sensitivity to phosphotyrosine phosphatase inhibitors, such as sodium orthovanadate (Ki = 1.07 ± 0.14 μM), bpV-PHEN (Ki = 0.38 ± 0.02 μM) and mpV-PIC (Ki = 0.39 ± 0.04 μM). Zn2+, an oxidizing agent, decreased the enzymatic activity in 50%. DTT and GSH, two reducing agents, enhanced the activity twofold. The non-invasive E. histolytica and free-living E. moshkovskii were less efficient in hydrolyzing p-NPP than the pathogenic E. histolytica suggesting that this enzyme could represent a virulence marker for this cell.