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 stud ies showed that the uptake of the nucleoside adenosine by purine-starv ed organisms was similar to 7-fold faster than by nutrient-replete cel ls. Further, these studies demonstrated that purine-starved organisms accumulated the nucleobases hypoxanthine and adenine at a rate >100-fo ld faster than organisms cultivated under replete conditions. Activiti es of several intracellular purine-salvage enzymes were measured in or ganisms from both culture conditions. Of those measured, the activitie s of adenine deaminase and hypoxanthine phosphoribosyltransferase were elevated similar to 4-fold and similar to 11-fold, respectively, in p urine-starved organisms. Competitive substrate specificity studies sug gested 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 transp orters expressed in response to purine starvation. These studies using C. luciliae may provide insights into the mechanisms of trypanosomati d adaptation to altered environments encountered during the course of the life cycle.