Formation of a complex containing ATP, Mg2+, and spermine -: Structural evidence and biological significance

The conformation of ATP in the presence of Mg2+ and/or spermine was studied by P-31 and H-1 NMR, to clarify how polyamines interact with ATP, Spermine predominantly interacted with the beta- and gamma-phosphates of ATP in the presence of Mg2+. A conformational change of the beta- and gamma-phosphate of ATP with spermine could not be observed in the absence of Mg2+ by P-31 NMR, It was found by H-1 NMR that the conformation of adenosine moiety of ATP was not influenced significantly by spermine. The binding of Mg2+ to ATP was slightly inhibited by spermine and vice versa, The results indicate that the binding sites of Mg2+ and spermine on ATP only partially overlap. The PotA protein, an ATP-dependent enzyme, was used as a model system to study the biological role of the ATP-Mg2+-spermine complex. The ATPase activity of PotA was greatly enhanced by spermine. Double reciprocal plots at several concentrations of spermine as an activator indicate that spermine interacts with ATP, but not with PotA The activity of protein kinase A was also stimulated about 2-fold by spermine. The results suggest that a ternary complex of ATP-Mg2+-spermine may play an important Pole in some ATP-dependent reactions in vivo and in the physiological effects of endogenous polyamines.