Cytidine 5'-triphosphate synthetase of calf liver. Size, polymerization, and reaction stoichiometry.

Calf liver CTP synthetase was purified 2000-fold from cytosol. The formation of 1 mol of CTP from UTP was accompanied by the cleavage of 1 mol of ATP to ADP and the formation of 1 mol of L-glutamate from L-glutamine. The stoichiometry of the liver enzyme reaction was identical with that found for the Escherichia coli B enzyme (Levitzki, A., and Koshland, D.E., Jr. (1971) Biochemistry 10, 3365-3371). The liver enzyme was also similar to the bacterial enzyme in that it polymerized in the presence of kinetically saturating levels of ATP and UTP. In the absence of nucleotides the enzyme had a sedimentation coefficient of 6.8 and an average molecular weight of 133,000 as determined by sedimentation and molecular sieving. In the presence of ATP and UTP, the enzyme had a sedimentation coefficient of 10.1 and a molecular weight, as determined by molecular sieving, of 263,000. The molecular weights of the two forms of the liver enzyme are about 25% higher than those of the corresponding forms of the bacterial enzyme (Long. C.W., Levitzki, A., and Koshland, D.E., Jr. (1970) J. Biol. Chem. 245, 80-87).