LOCALIZATION OF ACID-PHOSPHATASE-ACTIVITY ON THE SURFACE OF BLOOD-STREAM FORMS OF TRYPANOSOMA-CONGOLENSE

In vitro, living bloodstream forms of Trypanosoma congolense were show n to hydrolyse p-nitrophenyl phosphate, a substrate for phosphatases. This activity appears to be from an acid phosphatase because it was en hanced at low pH values, was inhibited by the acid phosphatase inhibit or 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 a ctivity 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 wit h the surface of the parasites, rather than with endocytic or intracel lular systems. This was supported by subcellular fractionation of radi olabelled parasites which showed some cosedimentation of acid phosphat ase activity with radiolabelled iodine. Histochemical studies of the p arasites also supported this conclusion. Electron microscopical examin ation of trypanosomes incubated with lead nitrate and p-nitrophenyl ph osphate 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 ph osphatase. (C) 1996 Academic Press, Inc.