Reactions of dysprosium with adenine nucleotides

Dysprosium catalyzes a rapid hydrolysis of both ATP and ADP, at ambient temperatures, pH 7.0, where no hydroxide precipitates. The reactive complexes, at pH 6.7, were found to contain 2Dy:1ATP and 3Dy:2ADP. AMP forms an insoluble complex containing 1Dy:2AMP, which does not hydrolyze. ATP also forms a soluble 1Dy:1ATP complex, which does not react. Dysprosium only catalyzes the hydrolysis of ATP above pH 5.8, where it has been titrated to the hydroxide. At the optimum pH (pH 7) the stoichiometric composition is Dy2.ATP.(OH)2, indicating that the active complex is neutral, whereas at pH 5.8 the stoichiometric composition is Dy2.ATP.(OH)+, indicating an inactive cationic complex. The mechanism proposed for the hydrolysis is consistent with those proposed for other in vitro systems known to catalyze the hydrolysis of ATP.