Isolation and Characterization of a Novel Bioactive Peptide, Carassius RFamide (C-RFa), from the Brain of the Japanese Crucian Carp

A novel bioactive peptide with the C-terminal RFamide was isolated from the brain of the Japanese crucian carp, Carassius auratus langsdorfii, by using the intestine of the fish as the bioassay system. The primary structure of the peptide was determined to be SPEIDPFWYVGRGVRPIGRFamide and it was designated Carassius RFamide (C-RFa). The sequence of C-RFa was found to be significantly homologous to the molluscan neuropeptide termed Achatina cardioexcitatory peptide 1 (ACEP-1). Both peptides have RPXGRFamide structure in their C-terminal moieties. C-RFa was found to have an excitatory effect on visceral muscle tissues of fish, newt, quail, and rat. In the stomach of the fish, Zacco temminckii, IGRFamide (C-RFa 17-20) was shown to be the minimal structure required for the excitatory effect and PIGRFamide (C-RFa 16-20) to be almost equipotent with the parent peptide C-RFa.