Elucidation of the fragmentation pathways of different phosphatidylinositol phosphate species (PIPx) using IRMPD implemented on a FT-ICR MS

This work reports on the fragmentation of phosphoinositides by tandem mass spectrometry (MS/MS) and MS³ experiments on a hybrid apex-Qe Fourier transform-ion cyclotron resonance mass spectrometer (FT-ICR MS) using internal infrared multiphoton dissociation (IRMPD). The fragmentation behavior of diacylphophatidylinositol triphosphate was intensively studied since an abundant loss of inositol biphosphate was observed. This loss was suggested to occur via phosphate migration along the inositol head group. Substantiation by MS³ experiments showed that this neutral loss is formed after the loss of water from the precursor ion, indicating phosphate migration along the inositol ring to the glycerol backbone. Further fragmentation of the ion formed by the loss of inositol biphosphate from diacylphophatidylinositol triphosphate resulted in the formation of a product ion with a molecular formula of C(3)H(5)O(7)P(2), corresponding to a glycerol backbone linked to two phosphate groups. We suggested different structures for this ion and compared their stability using modeling experiments.