Structural characterization of Arginine-vasopressin and Lysine-vasopressin by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and infrared multiphoton dissociation (IRMPD)

Arginine-vasopressin (AVP) and Lysine-vasopressin (LVP) were analyzed by reversed-phase liquid chromatography/mass spectrometry (LC-MS) using Fourier-transform ion cyclotron resonance (FT-ICR) MS electrospray ionization (ESI) in positive ion mode. LVP and AVP exhibited protonated adduct [M+H]+ as the predominant ion at m/z 1056.43965 and at m/z 1084.44561, respectively. Infrared multiphoton dissociation (IRMPD), using a CO2 laser source at a wavelength of 10.6 ?m, was applied to protonated vasopressin molecules. The IRMPD mass spectra presented abundant mass fragments essential for a complete structural information. Several fragment ions, shared between two target molecules, were discussed in detail. Some previously unpublished fragments were identified unambiguously utilizing the high resolution and accurate mass information provided by the FT-ICR mass spectrometer. The opening of disulfide loop and the cleavage of the peptide bonds within the ring were observed even under low energy fragmentation conditions. Coupling the high performance FT-ICR mass spectrometer with IRMPD as contemporary fragmentation technique proved to be very promising for the structural characterization of vasopressin.