Degradation of pyrimidines in Euglena gracills III. Ratio of uracil to thymine degradation

Abstract

In photoorganotrophically-grown cells of Euglena gracilis var. Z uracil (Ura) and thymine (Thy) were degraded in a fixed ratio of 1 : 4. The predominant degradation of Thy can be measured in vivo by the kinetics of Thy and Ura degradation, by the effect of catabolic intermediates at different concentrations and by double labelling experiments with [5− 3H]Ura and [2− 14C]Thy. In the latter type of experiment, 3H/ 14C of isolated dihydrouracil (DHUra) and dihydrothymine (DHThy) is respectively 1 10 of the starting promortion of precursors, suggesting a predominant degradation of Thy. Enhanced anabolic reactions of pyrimidine compounds can be produced by inhibition of degradation with dihydropyrimidines.