Fast atom bombardment and collisional activation mass spectrometry of retinyl phosphate mannose synthesized by liver membranes

Fast atom bombardment (FAB) and collisional activation dissociation (CAD) mass‐analysed ion kinetic energy (MIKE) spectra have confirmed the structures of retinyl phosphate (Ret‐P), retinyl phosphate mannose (Ret‐P‐Man) and guanosine 5′‐diphospho‐D‐mannose (GDP‐Man). Ret‐P‐Man was made in vitro while Ret‐P and GDP‐Man were chemically synthesized. Positive ion FAB mass spectrometry of Ret‐P showed an observable short‐lived spectrum with a mass ion at m/z 367 [M + H]⁺, and a major fragment ion at m/z 269 [M+HH₃PO₄]⁺. Negative ion FAB mass spectrometry of Ret‐P showed a strong stable spectrum with a parent ion at m/z 365 [MH]⁻, a glycerol (G) adduct ion at m/z 457 [MH+G]⁻ and a dimer ion at m/z 731 [2MH]⁻. GDP‐Man showed an intense spectrum with parent ion at m/z 604 [MH]⁻ and cationized species at m/z 626 [M+Na‐2H]⁻ and 648 [M+2Na‐3H]⁻. Negative ion FAB mass spectrometry of Ret‐P‐Man showed a parent ion at m/z 527 [MH]⁻ and a fragment ion at m/z 259 [C₆H₁₂PO₉]⁻. The CAD‐MIKE spectra showed structurally significant fragment ions at m/z 442 and 361 for the [MH]⁻ ion of GDP‐Man, and at m/z 509, 406, 364 and 241 for the [MH]⁻ ion of Ret‐P‐Man. FAB and CAD‐MIKE spectra have been applied successfully to confirm the structure of Ret‐P‐Man made in vitro from Ret‐P and GDP‐Man.