Enzyme Regulation in a Trypanosomatid: Effect of Purine Starvation on Levels of 3′-Nucleotidase Activity

Abstract

Crithidia fasciculata, a nonpathogenic relative of the leishmanial and trypanosomal pathogens of humans and animals, showed a 3'-ribonucleotidase activity similar to that in Leishmania donovani. The level of 3'-nucleotidase activity in Crithidia was regulated by the availability of purines in the culture medium. Specifically, organisms obtained from culture medium depleted of purines contained elevated levels of enzyme activity compared to those grown in complete medium. The 3'-nucleotidase, located at the cell surface, may serve as a first step in purine salvage for these protozoa, which are unable to synthesize the purine ring de novo.