Figure 5. Extracted MS/MS spectra for m/z 558.0644, detected in ESI (−) mode at three collision energies: 10, 20, 40 eV.

The empirical formula corresponding to the neutral mass, C₁₅H₂₃N₅O₁₄P₂ corresponds to a compound with a single database entry in METLIN and annotated as N1-(5-phospho-D-ribosyl)-AMP (pRib-AMP). MS/MS spectra were collected for this compound from: (A) the chemically derivitized cADPR product, pRib-AMP, and, (B) an IRBC sample.