[13] CTP synthetase of bovine calf liver

This chapter focuses on the cytidine triphosphate (CTP) synthetase of bovine calf liver. The enzyme purified from rat liver and bovine liver utilizes uracil triphosphate (UTP), and the product is CTP. The stoichiometry of the reaction is the same as that of the reaction catalyzed by the Escherichia coli B enzyme, and in both cases, guanosine triphosphate (GTP) is a strong activator. There is evidence that a CTP synthetase is present in other mammalian cells. The rate of the formation of CTP can be determined by two methods. In the first method, CTP formation is followed by an increase in absorbance at 290 nm, because uridine nucleotides are almost completely transparent at this wavelength. In the second method, the formation of labeled CTP from [2-14C] UTP is measured. Despite the identical stoichiometries and similar polymerizing properties, the enzymes have markedly different kinetic properties. There is evidence that a CTP synthetase is present in other mammalian cells.