OCCURRENCE OF ANALOGS OF THE MYOTROPIC NEUROPEPTIDE ORCOKININ IN THE SHORE CRAB, CARCINUS-MAENAS - EVIDENCE FOR A NOVEL NEUROPEPTIDE FAMILY

By use of an enzyme immunoassay that was developed for the determinati on of orcokinin, a myotropic neuropeptide of the sequence NFDEIDRSGFGF N from the crayfrsh, Orconectes limosus, immunoreactive material was d etected in extracts of thoracic ganglia from the share crab, Carcinus maenas. Isolation of the immunoreactive material was achieved by the f ollowing steps: 1) prepurification by gel filtration, 2) immunoaffinit y chromatography on an anti-orcokinin IgG protein-A sepharose column, and 3) reversed-phase HPLC. The HPLC profile after affinity purificati on revealed three main immunoreactive peptides that were rechromatogra phed. None of these peptides was identical to orcokinin in terms of re tention time. Automated gas-phase sequencing revealed these peptides t o be analogues of orcokinin differing in one amino acid residue. They were named [Ser(9)]-, [Ala(13)]- and [Val(13)]orcokinin (NFDEIDRSSFGFN , M(r) 1549.3; NFDEIDRSGFGFA, M(r) 1475.3; NFDEIDRSGFGFV, M(r) 1503.9) . Carboxypeptidase A treatment of the peptides indicated a free C-term inus. Complete characterization of the three peptides was achieved fro m approximately 230 thoracic ganglia of Carcinus maenas.