Characterization of cyclic ADP-ribose and 2′-phospho-cyclic-ADP-ribose by 31P NMR spectroscopy

The 31P NMR spectra of the Ca2+ mobilizing nucleotides cyclic ADP-ribose and 2′-phosphocyclic ADP-ribose have been studied. Both nucleotides show doublets of doublets in the range −9.5 to −11 ppm for the pyrophosphate group. The P-cADPR exhibits a singlet in the 0 to +4 ppm range for the 2′-phospho group. The pH dependence of the 31P signals shows transitions with pKa values of 8.37 and 8.95 for cADPR and P-cADPR, respectively.