title: Matrix-assisted laser desorption/ionization fourier transform mass spectrometry for the identification of orcokinin neuropeptides in crustaceans using metastable decay and sustained off-resonance irradiation.
abstract: Vacuum UV matrix-assisted laser desorption/ionization (MALDI) Fourier transform ion cyclotron resonance mass spectrometry (FTMS) has been applied to the direct analysis of crustacean neuronal tissues using in-cell accumulation techniques to improve sensitivity. In an extension of previous work by Li and co-workers (Kutz, K. K.; Schmidt, J. J.; Li, L. Anal. Chem. 2004, 76, 5630-5640), and with a focus on the Maine lobster, Homarus americanus, we report that many peaks appearing in direct tissue spectra from crustaceans result from the metastable decay of aspartate-containing neuropeptides with localized protonation sites. We report on mass spectral characteristics of crustacean neuropeptides under MALDI-FTMS conditions and show how fragments formed by Asp-Xxx cleavages can be used to advantage for the identification of orcokinin peptides, a ubiquitous family of crustacean neuropeptides with a highly conserved N-terminus sequence. We show that predicted fragment ion fingerprints (FIFs) can be used to screen internally calibrated direct tissue spectra to provide high-confidence identification of previously identified orcokinin peptides. We use FIFs, identified based upon characteristic neutral losses, to screen for new members of the orcokinin family. Sustained off-resonance irradiation of y-series fragment ions is used to sequence the variable C-terminus. We apply these techniques to the analysis of CoG tissues from Cancer borealis and Panulirus interruptus and show that orcokinins in P. interruptus were misidentified in a previous MALDI-TOF study.
authors.affiliation: Department of Chemistry, Bowdoin College, Brunswick, Maine 04011, USA. estemmle@bowdoin.edu
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Stemmler
authors.forename: Heather L
authors.initials: HL
authors.lastname: Provencher
authors.forename: Maureen E
authors.initials: ME
authors.lastname: Guiney
authors.forename: Noah P
authors.initials: NP
authors.lastname: Gardner
authors.forename: Patsy S
authors.initials: PS
authors.lastname: Dickinson
mesh_terms: D000818:Animals; D033364:Decapoda / Q000737:chemistry*; D007834:Lasers; D009479:Neuropeptides / Q000032:analysis* / Q000737:chemistry / Q000528:radiation effects; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation / Q000379:methods*; D014466:Ultraviolet Rays
chemical_list: D009479:Neuropeptides; C079067:orcokinin