Catabolism of deoxythymidylate in some trypanosomatids

Abstract

An initial observation converning the failure of [3H]thymidine at high specific activity to be incorporated into the DNA ofCrithidia fasciculatafor more than a brief intitial period has been correlated with the presence at high specific activity in the organism of thymidine phosphorylase activity with an equilibrium in the direction of catabolism. This enzyme degrades thymidine to thymine which is not utilized by the organism. The enzyme has also been shown to be present in a number of other trypanosomatids, including the culture forms ofTrypanosoma cruzi, where the specific activity was nearly as high as that inC. fasciculata.Evidence is presented that inC. fasciculata, the culture forms ofT. cruziand possibly other species of trypanosomatid, the thymidine phosphorylase, together with a thymidylate phosphatase, forms a catabolic pathway which degrades thymine nucleotides to thymine, which is then excreated. About 60% of the thymine nucleotides made by organisms appear to be matabolized through the pathway, suggesting that their synthesis is not subject to completely effective regulatory control.