J. Biol. Chem., Vol. 259, Issue 15, 9379-9383, 08, 1984

Characterization of ATP complexes with lanthanide (III) ions

CD Eads, P Mulqueen, WD Horrocks Jr and JJ Villafranca

Several spectroscopic techniques are used to investigate the stoichiometry and properties of ATP complexes with lanthanide(III) (Ln(III)], ions. The ATP2-lanthanide(III) complex predominates at millimolar ATP levels and dissociates to the 1:1 complex with a Kd of 300 +/- 50 microM for the Eu(III) case. Two independent techniques, viz. field-dependent water proton relaxation for the Gd(III) complex and metal ion luminescence lifetime measurements for the Eu(III) complex, yield a value of approximately 2 for the number of water molecules coordinated to the metal ion. The latter technique yields an approximate metal-ion hydration number of 4 for the 1:1 complex. Dynamic properties of the Gd(III) X ATP2 complex including the temperature dependence of correlation times describing rotation of the complex and ATP exchange have been studied by field-dependent water- proton relaxation and by temperature-dependent 31P NMR relaxation studies. These data are consistent with formation of a 2:1 ATP- lanthanide complex at millimolar ATP concentrations. Other types of complexes are detected under conditions in which there is insufficient ATP to satisfy the 1:2 metal:nucleotide stoichiometry.
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