STRUCTURE AND DYNAMICS OF ADENOSINE TRIPHOSPHATE-AL(III) COMPLEXES ATPH 7.4

The interaction of Al(III) with adenosine 5'-triphosphate (ATP) was in vestigated at pH = 7.4 by P-31, C-13, H-1, and Al-27 NMR. Two complexe s coexist in equilibrium: 2:1 and a 1:1 complexes, Al(III)(ATP)2 and A l(III)(ATP). Their phenomenological equilibrium constants of formation were calculated from the P-31 NMR data. They are in good agreement wi th independently determined thermodynamic equilibrium constants (Kiss, T.; Sovago, I.; Martin, R. B. Inorg. Chem. 1991, 30, 2130-2132). The exchange rate between free and Al(III)-bound ATP (in the 2:1 complex) was determined from a P-31-P-31 EXSY experiment to be 3.4 s-1 at 295 K , a value diagnostic of a dissociative mechanism from octahedral Al(II I). The rate of exchange is probably governed by the rupture of the AI (III)-phosphate bonds, the Al(III)-ATP 1:1 complex being an intermedia te in the exchange process. The P-31 NMR resonances of the complexes a re broad. In the case of the 2:1 complex, since the line widths are li nearly related to the square of the field of observation, while the lo ngitudinal relaxation rates are independent of this field, the broaden ing could be ascribed to relatively fast exchange of two or more forms of this 2:1 complex. At 270 K, at least four signals could be observe d for the complexed beta-P-31. The possible attribution of these signa ls to various diastereoisomers of the 2:1 complex is discussed.