Enhanced acquisition of purine nucleosides and nucleobases by purine-starved Crithidia luciliae

The effects of purine starvation on the ability of the trypanosomatid Crithidia luciliae to accumulate purines were determined. Kinetic studies showed that the uptake of the nucleoside adenosine by purine-starved organisms was approximately 7-fold faster than by nutrient-replete cells. Further, these studies demonstrated that purine-starved organisms accumulated the nucleobases hypoxanthine and adenine at a rate > 100-fold faster than organisms cultivated under replete conditions. Activities of several intracellular purine-salvage enzymes were measured in organisms from both culture conditions. Of those measured, the activities of adenine deaminase and hypoxanthine phosphoribosyltransferase were elevated approximately 4-fold and approximately 11-fold, respectively, in purine-starved organisms. Competitive substrate specificity studies suggested that these elevated enzyme activities were not responsible for the increased rates of uptake by purine-starved cells. The results are consistent with the induction of novel surface membrane purine transporters expressed in response to purine starvation. These studies using C. luciliae may provide insights into the mechanisms of trypanosomatid adaptation to altered environments encountered during the course of the life cycle.