The detection of red pigment-concentrating hormone (RPCH) in crustacean eyestalk tissues using matrix-assisted laser desorption/ionization–Fourier transform mass spectrometry: [M + Na]+ ion formation in dried droplet tissue preparations
Article first published online: 18 JAN 2006
Copyright © 2006 John Wiley & Sons, Ltd.
Journal of Mass Spectrometry
Volume 41, Issue 3, pages 295–311, March 2006
How to Cite
Stemmler, E. A., Gardner, N. P., Guiney, M. E., Bruns, E. A. and Dickinson, P. S. (2006), The detection of red pigment-concentrating hormone (RPCH) in crustacean eyestalk tissues using matrix-assisted laser desorption/ionization–Fourier transform mass spectrometry: [M + Na]+ ion formation in dried droplet tissue preparations. J. Mass Spectrom., 41: 295–311. doi: 10.1002/jms.989
- Issue published online: 14 MAR 2006
- Article first published online: 18 JAN 2006
- Manuscript Accepted: 18 NOV 2005
- Manuscript Received: 10 SEP 2005
- National Science Foundation. Grant Numbers: MRI-0116416, IBN-0111040.
- Coles and Doherty Summer Research Fellowships.
- Howard Hughes Medical Institute.
Red pigment-concentrating hormone (RPCH), an octapeptide found in crustaceans and insects with the sequence pGlu-Leu-Asn-Phe-Ser-Pro-Gly-Trp-NH2, is an N- and C-terminally blocked uncharged peptide. These structural features are shared with many members of the larger adipokinetic hormone (AKH)/RPCH peptide family in insects. We have applied vacuum UV matrix-assisted laser desorption/ionization (MALDI)-Fourier transform ion cyclotron mass spectrometry (FTMS) to the direct analysis of crustacean sinus gland tissues, using 2,5-dihydroxybenzoic acid (DHB) as the MALDI matrix, and have found that RPCH is detected in the cationized, [M + Na]+, form under conditions where other peptides in the direct tissue spectra are protonated without accompanying [M + Na]+ or [M + K]+ satellite peaks. The [M + H]+ ion for RPCH is not detected in tissue samples or for an RPCH standard, even when care is taken to eliminate metal ions. This behavior is not unprecedented; however, both direct tissue spectra and SORI-CID spectra provide no clues to suggest that the ionizing agent is a metal cation. In this communication, we characterize the MALDI-FTMS ionization and SORI-CID mass spectra of the [M + Na]+ and [M + K]+ ions from RPCH, and report on the detection of this neuropeptide in sinus gland tissues from the lobster Homarus americanus and the kelp crab Pugettia producta. We describe two strategies, an on-probe extraction procedure and a salt-doping approach, that can be applied to previously analyzed MALDI tissue samples to enhance and unmask sodiated peptides that may otherwise be mistaken for novel neuropeptides. Copyright © 2006 John Wiley & Sons, Ltd.