The kinetics and feedback inhibition of cytidine 5'-triphosphate synthetase in wild-type and mutant Chinese hamster cells.

The kinetics and cytidine 5'-triphosphate (CTP) feedback inhibition of CTP synthetase in wild-type and four mutants of Chinese hamster V79 cells have been studied. The enzymes of the wild type and three of the four mutants exhibited positive cooperativity with the substrate uridine 5'-triphosphate (UTP). Three of the mutants had Kmapp and S50 values distinctly greater than those of the wild type, while the fourth mutant had values similar to those of the wild type. All four mutants exhibited resistance to CTP feedback inhibition, while the wild type was sensitive to such inhibition. It is postulated that a single mutational event in each mutant had caused a concomitant change of the enzyme in its binding both to the substrate UTP and to the end-product CTP.