Isolation of two FMRFamide-related peptides from crayfish pericardial organs.

Pericardial organs of the crayfish, Procambarus clarkii, were removed, and material from them was extracted and fractionated using two sequential reverse-phase HPLC columns. Fractions were analysed using a radioimmunoassay (RIA) specific for the C-terminal peptide sequence -Arg-Phe-NH2. The peak immunoreactive fraction from the second column appeared to contain two peptides with the sequences DRNFLRFamide and NRNFLRFamide, based on microsequencing analysis and on the absolute requirement for the amide in the RIA. These two peptides, respectively, have been given the names NF1 and DF2 due to similarity with previously identified lobster peptides F1 and F2. NF1 and DF2 are cardioexcitatory and augment synaptic transmission at a neuromuscular synapse, and evidence is presented for the calcium-dependent release of these peptides from the pericardial organs.