FIG. 1.

Purine uptake and salvage in Leishmania promastigotes. The large oval represents the cell surface membrane of the parasite. The four purine transporters that have been identified in L. donovani and L. major are indicated as NT1, NT2, NT3, and NT4, with their substrates indicated in parentheses (Ado, adenosine; Pyr, pyrimidine nucleosides; Ino, inosine; Guo, guanosine; Hyp, hypoxanthine; Xan, xanthine; Ade, adenine; Gua, guanine). The function of NT4 is currently under investigation. The purine salvage pathway is indicated schematically, with arrows representing the interconversion of individual purines (14).