In this work, we describe how living cells of Trypanosoma brucei procyclic forms were able to hydrolyze extracellular p-nitrophenylphosphate (pNPP). These intact parasites, which had their viability determined by motility and the Trypan blue method, presented a low level of pNPP hydrolysis in the absence of any divalent metal (0.72 +/- 0.07 nmol pNP/mg min). Interestingly, in the presence of 5 mM MgCl2, ectophosphatase activity of 1.91 +/- 0.21 nmol pNP/mg min was observed. The ectophosphatase activity was also stimulated by MnCl2, CoCl2 and CuCl2 but not by CaCl2 and CdCl2? and was inhibited by ZnCl2. The addition of Mg2+, Mn2+, Co2+ and Cu2+ to extracellular medium increased the ectophosphatase activity in a dose-dependent manner. At 5 mM pNPP, half-maximal stimulation of pNPP hydrolysis was obtained with 0.39 +/- 0.05 MM MgCl2, 0.33 +/- 0.03 mM MnCl2, 1.63 +/- 0.12 mM CoCl2, and 2.04 +/- +/- 0.33 MM CuCl2. In the absence of any divalent metal (basal activity) the apparent K-m for pNPP was 0.66 +/- 0.09 mM, while at saturating MgCl2 concentrations the corresponding apparent K-m for pNPP for Mg2+ -stimulated phosphatase activity (difference between total minus basal phosphatase activity) was 0.27 +/- 0.03 mM. The Mg2+-stimulated pNPP hydrolysis was strongly inhibited by ZnCl2 and vanadate, while the metal-independent basal phosphatase activity was less inhibited by these phosphotyrosyl phosphatase inhibitors. (C) 2003 Elsevier B.V. All rights reserved.118416711928