The apparent ionization constants of the adenosinephosphates and related compounds.

The central r81e of the adenosinephosphates in biochemical mechanisms depends upon their phospholylation and dephosphorylation reactions (l3). The equilibria of these reactions depend upon pH, and therefore information concerning the various ionization constants is of fundamental importance. With the aid of the various ionization constants it, is possible (a) to calculate the variation in the equilibrium constant or free energy of reaction with pH and (b) to calculate the number of equivalents of acid or base produced by the reaction per mole of reactant. Dixon (3) has recently discussed the variation of the energy of the energy-rich phosphate bond with pH. Hill and Morales (4) have pointed out, the importance of the electrostatic factor in the high energy of the phosphate bond in adenosinetriphosphate (ATP) and its relation to the various ionization constants. In the case of adenosinediphosphate (ADP) and ATP there is a paucity of satisfactory titration data on material of known purity. Preliminary titrations have been carried out by Eirich and Filz (5) and Lohmann (6). A number of phosphoric acid esters of biological importance have been titrated by Meyerhof and Lohmann (7), Kiessling (8), and Cori, Colowick, and Cori (9). Kumler and Eiler (10) have determined the ionization constants of alkyl phosphates and discussed the factors affecting the ionization constants of phosphate esters.