Gas-Phase Internal Ribose Residue Loss from Mg-ATP and Mg-ADP Complexes: Experimental and Theoretical Evidence for Phosphate-Mg-Adenine Interaction.

Gas-phase decompositions of magnesium complexes with adenosine-5'-triphosphate (ATP) and adenosine-5'-diphosphate (ADP) were studied by using electrospray ionization-collision-induced dissociation-tandem mass spectrometry, in the negative ion mode. The loss of internal ribose residue was observed and was found to occur directly from the [ADP-3H+Mg] ion. The occurrence of this process indicates the presence of a strong phosphate-Mg-adenine interaction. The performed quantum mechanics calculations confirmed the occurrence of this interaction in the [ADP-3H+Mg] ion, namely the presence of Mg-N7 bond and hydrogen bond between the phosphate oxygen atom and amino group. Although the finding concerns the gas phase, it indicates that phosphate-Mg-adenine interaction may be also of importance for biological processes. The loss of an internal ribose residue was also observed for calcium and zinc complexes with ATP/ADP as well as for magnesium complexes with guanosine-5'-triphosphate (GTP) or guanosine-5'-diphosphate (GDP). Therefore, it is reasonable to conclude that the presence of the phosphate-metal-nucleobase interaction is a feature of gas phase [NDP-3H+metal] ion (NDP, nucleoside-5'-diphosphate) and may also be important for biological processes.