The crustacean stomatogastric
ganglion (STG) is modulated by both locally released neuroactive compounds and circulating
hormones. This study presents mass spectrometric characterization of the
complement of
peptide hormones present in one of the major neurosecretory structures, the pericardial organs (POs), and the detection of
neurohormones released from the POs. Direct
peptide profiling of
Cancer borealis PO tissues using matrix-assisted
laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) revealed many previously identified
peptides, including
proctolin,
red pigment concentrating hormone (
RPCH),
crustacean cardioactive peptide (CCAP), several orcokinins, and
SDRNFLRFamide. This technique also detected
corazonin, a well-known
insect hormone, in the POs for the first time. However, most mass spectral peaks did not correspond to previously known
peptides. To characterize and identify these novel
peptides, we performed MALDI postsource decay (PSD) and electrospray ionization (ESI) MS/MS de novo sequencing of
peptides fractionated from PO extracts. We characterized a truncated form of previously identified
TNRNFLRFamide, NRNFLRFamide. In addition, we sequenced five other novel
peptides sharing a common C-terminus of RYamide from the PO
tissue extracts. High K+ depolarization of isolated POs released many
peptides present in this tissue, including several of the novel
peptides sequenced in the current study.