Urotensin II in Invertebrates: From Structure to Function in Aplysia californica
(A) Representative MALDI MS spectrum of individual cultured buccal sensory neurons expressing FMRFa, FRFa and apUII prohormones. apUII-derived peptides (in bold), FMRFa, FRFa peptides (a–e) and an apUII linker peptide are labeled. The inset table specifies the accuracy of the apUII peptides measurement; (M+H) is the monoisotopic mass of the protonated molecular ions, (*) denotes the theoretical mass corrected for the difference from the disulfide bond. (B) Fragmentation spectrum of apUII peptide S -S  detected in a +2 charge state with the two red Cys residues highlighted (lower case c). (C) Fragmentation spectrum of apUII peptide S -Q  detected in a +2 charge state.