Vibrational study of phosphate modes in GDP and GTP and their interaction with magnesium in aqueous solution

Raman and infrared spectra were examined for guanosine 5′-diphosphate (GDP) and guanosine 5′-triphosphate (GTP) in aqueous solution. The vibrational modes were assigned on the basis of isotopic frequency shifts and relative intensities in the Raman and infrared spectra. The observed frequency shifts on ¹⁸O isotope labeling made it possible to identify the bands from each phosphate group (α, β, γ). Frequency shifts were observed as Mg²⁺ complexes with GDP and GTP. The results suggested that Mg²⁺ binds to GDP in a bidentate manner to the α, β P · · O bonds and in a tridentate manner to the α, β and γ P · · O bonds of Mg·GTP. The results indicate that structure of Mg²⁺ coordinated to GTP in aqueous solution differs somewhat to that found for Mg·ATP. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 219–227, 1998