Localisation of acid phosphatase activity on the surface of bloodstream forms of Trypanosoma congolense

In vitro, living bloodstream forms of Trypanosoma congolense were shown to hydrolyse p-nitrophenyl phosphate, a substrate for phosphatases. This activity appears to be from an acid phosphatase because it was enhanced at low pH values, was inhibited by the acid phosphatase inhibitor sodium fluoride, and was not inhibited by the alkaline phosphatase inhibitor tetramisole. The activity did not appear to be secreted into the surrounding medium by the living parasites although phosphatase activity could be detected in the surrounding medium when dead or dying parasites were present. Studies at various temperatures indicated that at least some of this acid phosphatase activity may be associated with the surface of the parasites, rather than with endocytic or intracellular systems. This was supported by subcellular fractionation of radiolabelled parasites which showed some cosedimentation of acid phosphatase activity with radiolabelled iodine. Histochemical studies of the parasites also supported this conclusion. Electron microscopical examination of trypanosomes incubated with lead nitrate and p-nitrophenyl phosphate showed lead phosphate deposits on the surface of the parasites in addition to the expected localisation in the flagellar pocket. We conclude that Trypanosoma congolense possesses a surface-bound acid phosphatase.