Initial studies of the enzymatic constituents of an isolated surface membrane fraction of the human pathogen Leishmania donovani, the causative agent of visceral leishmaniasis (Kala-azar), have demonstrated a 3 feet-nucleotidase activity. A further study of this enzyme is warranted and of significance for the following reasons: i) the enzyme is extremely active and is disposed at the parasite surface, ii) the enzyme is capable of contributing to the essential purine salvage pathway of these parasites which lack the ability to synthesize purines de novo, and iii) specific 3 feet-nucleotidases are not associated with mammalian cells and tissues. A major goal of this proposal, therefore, is to isolate the 3 feet-nucleotidase in pure form and in amounts which are adequate for physical-chemical and kinetic characterizations that will include the study of: molecular weight, amino acid and carbohydrate composition, subunit structure, substrate specificity, and inhibitors and activators. The physiological role of the leishmanial 3 feet-nucleotidase will be studied, in particular with regard to its function in the parasite's acquisition of preformed purines from impermeable ribonucleotides. In addition, this leishmanial enzyme will be examined for its diagnostic potential, both on the basis of its enzymatic activity and as a specific surface antigen. The results of this study will provide new information on the leishmanial 3 feet-nucleotidase which may be useful in the clinical diagnosis of leishmanial infection and for the design of effective chemotherapeutic agents.