NOVEL TACHYKININS FROM THE BRAIN OF THE SEA LAMPREY, PETROMYZON-MARINUS, AND THE SKATE, RAJA-RHINA

Using radioimmunoassay for mammalian tachykinins, peptides with substa nce P-like immunoreactivity and neurokinin A-like immunoreactivity wer e identified in an extract of the brain of the longnose skate, Raja rh ina (elasmobranch) but only a peptide with neurokinin A-like immunorea ctivity was identified in the brain of the sea lamprey, Petromyzon mar inus (agnathan). The primary structure of the skate peptide with subst ance P-like immunoreactivity (Ala-Lys-His-Asp-Lys-Phe-Tyr-Gly-Leu-Met- NH2) shows one amino acid substitution (Phe(3) --> His) compared with scyliorhinin I, previously isolated from dogfish brain and gut. The sk ate neurokinin A-related peptide (His-Lys-Leu-Gly-Ser-Phe-Val-Gly-Leu- Met-NH2) shows tow substitutions (Thr(3) --> Leu and Asp(4) --> Gly) c ompared with mammalian neurokinin A. Although the COOH-terminus of the lamprey tackhykinin g-Lys-Pro-His-Pro-Lys-Gly-phe-Val-Gly-Leu-Met-NH2 ) resembles neurokinin A, the presence of the strongly conserved Lys/A rg-Pro-Xaa-Pro motif at the NH2-terminus of the peptide indicates grea ter structural similarity with substance P. The additional arginine re sidue at position 1 in the peptide suggests that the lamprey is utiliz ing a site of postranslational processing in the tachykinin precursor that is different from the equivalent site in mammalian and other lowe r vertebrate preprotachykinin(s).