Surface membrane localization of 3'- and 5'-nucleotidase activities in Leishmania donovani promastigotes.

Distinct 3'- and 5'-nucleotidase activities were localized to the surface membrane of Leishmania donovani promastigotes using enzymatic reactions with live intact cells and fine structure enzyme-mediated cytochemical reactions with intact cells, cell homogenates, and isolated surface membranes. The results indicated that virtually all activity of both enzymes was restricted to the parasite surface membrane. Cytochemical localization results demonstrated that both activities were externally disposed on the intact organism, and were restricted to the external face of the isolated parasite surface membrane. The two activities were cytochemically differentiated by their substrate specificities and sensitivity to several inhibitors. On the basis of their cytochemical sensitivity to glutaraldehyde treatment, the two nucleotidase enzymes were distinguished from another external surface membrane enzyme, a nonspecific acid phosphatase. Results of the cytochemical assays further demonstrated the biochemical and structural asymmetry of the isolated parasite surface membrane with regard to the localization and distribution of the active sites of these two enzymes.