A Novel Ecto-Phosphatase Activity ofHerpetomonas muscarum muscarumInhibited by Platelet-Activating Factor

Abstract

In the present work ecto-phosphatase activity inHerpetomonas muscarum muscarumhas been characterized using live parasites. This enzyme hydrolyzedp-nitrophenylphosphate at a rate of 4.27 nmol Pi/mg of protein · min. A pH curve was generated, in which these intact flagellates showed the highest phosphatase activity at pH 6.5. Classical inhibitors for acid phosphatase, such as sodium orthovanadate, sodium tartrate, and ammonium molybdate, were used in the experiments and showed different patterns of inhibition. Lithium fluoride, aluminum chloride, and fluoroaluminate complexes were also tested. Although lithium fluoride and fluoroaluminate complexes were capable of inhibiting the phosphatase activity, aluminum chloride stimulated this enzyme. Cytochemical analysis showed the localization of this enzyme on the parasite surface. This ecto-phosphatase activity was also significantly diminished when the parasites were treated with 10−6M platelet-activating factor (PAF), a potent phospholipid mediator that promoted cellular differentiation in this parasite.