Purine stress in crithidia: adaptation of a parasite to environmental stress.

How parasitic protozoa survive varying nutrient levels is a key issue in parasitology. Here, Annette Gero explains how the Trypanosomatid Crithidia luciliae responds to purine stress by increasing the rates of transport of nucleosides and bases from the environment and by increasing the activity of the ectoenzyme 3'-nucleotidase (3'NTase), which breaks down external nucleotides so that they can be salvaged as nucleosides. The increase in activity of the purine transporters, and the 3'NTase activity is simultaneous with a general increase in the purine metabolic pathway, hence ensuring that purines are readily available to the parasite during purine stress.