Regulation of ribonucleotide reduction by deoxyribonucleotides in intact Chinese hamster ovary cells

The ribonucleotide reductase model of Thelander and Reichard, which is based on studies of the purified enzyme, has been tested in cultured Chinese hamster ovary K-1 cells. Deoxyribonucleoside triphosphate concentrations were manipulated by the use of drugs or naturally occurring deoxyribonucleosides, and ribo- and deoxyribo-nucleoside triphosphate concentrations were measured. The results are consistent with the hypothesis that dTTP inhibits CDP reduction and stimulates GDP reduction, and that dGTP inhibits CDP reduction. However, the results are contrary to the hypothesis that dGTP inhibits UDP reduction and stimulates ADP reduction, and that dATP inhibits CDP reduction. It is concluded that the model of Thelander and Reichard applies only in part to intact CHO cells.