Purine Metabolism in Trypanosomatids*

Abstract

Purine nucleotide biosynthesis was studied in culture forms of Trypanosoma cruzi strain Y, Crithidia deanei (a reduviid trypanosomatid with an endosymbiote) and an aposymbiotic strain of C. deanei (obtained by curing C. deanei with chloramphenicol). T. cruzi synthesized purine nucleotides only from the preformed bases adenine (A) and guanine (G) (salvage pathway), A being incorporated into both A and G nucleotides. Similar results were obtained with G, indicating that this flagellate has a system for the interconversion of purine nucleotides. C. deanei synthesized purine and pyrimidine nucleotides from Gly (de novo pathway) and purine nucleotides from A and G (salvage pathway). A was incorporated into both A and G nucleotides, while G was incorporated into G nucleotides only, indicating the presence of a metabolic block at the level of GMP reductase. The aposymbiotic C. deanei strain was unable to utilize Gly for the synthesis of purine nucleotides, although Gly was utilized for synthesizing pyrimidine nucleotides. The endosymbiote is implicated in the de novo purine nucleotide pathway of the C. deanei-endosymbiote complex. The incorporation of A and G by aposymbiotic C. deanei strain followed a pattern similar to that observed for C. deanei.