A Kinetic Study of Carbamyl Phosphate Synthetase.

While it is clear from the stoichiometry of the over-all reaction (Reaction 3) that 2 moles of ATP are utilized per mole of carbamyl phosphate formed (l), equilibrium dialysis experiments indicated that only 1 mole of ATP was bound per mole of enzyme in the absence of acetylglutamate (2). In order to gain more information about the nature of ATP binding by carbamyl phosphate synthetase, kinetic and other studies were carried out. In this paper, evidence will be presented which shows that there are two sites for ATP binding on the enzyme, of which one is independent of the binding of other substrates and the other site requires prior binding of acetylglutamate.