Ap4A is not an efficient Zn(II) binding agent. A concerted potentiometric, calorimetric and NMR study

Diadenosine 5′,5″-P1P4 tetraphosphate (Ap4A) has been considered as an intracellular partner for Zn(II). We applied potentiometry, ITC and NMR to study protonation equilibria of Ap4A and Zn(II) complexation by this dinucleotide. The values of binding constants obtained by these three techniques under various experimental conditions coherently demonstrated that Ap4A binds Zn(II) weakly, with an apparent binding constant of ca. 104 at neutral pH. Such a low stability of Zn(II) complexes with Ap4A excludes a possibility for interactions between these two agents in vivo.