The ability to identify neuropeptides in crustacean neuronal tissue samples has been advanced through the application of mass spectrometry. The identification of neuropeptides and the determination of conserved and variable sequences in neuropeptides families, coupled with electrophysiological characterization of neuropeptides responses, provides insights into regions of the peptide sequence that may be responsible for activity. Recent study have demonstrated that matrix assisted laser desorption/ionization (MALDI)-Fourier transform mass spectrometry (FTMS) presents advantages over MALDI-time of flight MS for the direct analysis of tissue samples (Kurtz et al., Anal. Chem. 2004, 76, 5630). The high resolution capabilities of FTMS, coupled with mass measurement accuracy, are particularly important when analyzing complex mixtures of neuropeptides found in crustacean tissue samples. The longer time frame associated with MALDI-FTMS detection additionally results in peptide fragmentation via small neutral losses and cleavages C-terminal to aspartate residues for charge localized peptides (Stemmler et al., Anal. Chem. 2005, 77 3594), and these fragmentation reactions can be used to facilitate the identification of members of peptide families susceptible to this mode of fragmentation. In this study, we describe recent work on the identification of orcokinin family peptides in different decapod crustaceans, and show how metastable decomposition under MALDI-FTMS conditions can be used to provide high confidence comparative measurements for members of this peptide family. We present data on conserved and variable sequences for neuropeptides identified in the commissural ganglion and sinus glands of five decapod crustacean species.
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