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Secreted Phosphatase Activities in Trypanosomatid Parasites of Plants Modulated by Platelet-Activating Factor

First, second, third, fourth, and eighth authors: Instituto de Microbiologia Professor Paulo de Góes, UFRJ, Ilha do Fundão, Rio de Janeiro, 21941-590; fifth, sixth, and seventh authors: Instituto de Biofísica Carlos Chagas Filho, ICB; and ninth author: Departamento de Bioquímica Médica, ICB, UFRJ, Ilha do Fundão, Rio de Janeiro, 21941-590 Brazil

The secreted phosphatase activities of two trypanosomatid parasites were characterized and compared with supernatants of living cells. The plant parasite Phytomonas françai and the phytophagous hemipteran parasite Herpetomonas sp. hydrolyzed p-nitrophenylphosphate at a rate of 15.54 and 6.51 nmol Pi/mg of protein per min, respectively. Sodium orthovanadate (N_aVO₃) and sodium fluoride (NaF) decreased the phosphatase activities. The phosphatase activity of P. françai was drastically diminished (73% inhibition) in the presence of sodium tartrate, whereas the phosphatase activity of Herpetomonas sp. was inhibited by 23%. Cytochemical analysis showed the localization of these enzymes on the external surface and in the flagellar pocket of the two trypanosomatids. Sodium tartrate inhibited this reaction, confirming the biochemical data. Platelet-activating factor modulated the phosphatase activities, inhibiting P. françai activity and stimulating Herpetomonas sp. phosphatase activity.