TACHYKININS WITH UNUSUAL STRUCTURAL FEATURES FROM A URODELE, THE AMPHIUMA, AN ELASMOBRANCH, THE HAMMERHEAD SHARK, AND AN AGNATHAN, THE RIVER LAMPREY

Tachykinins were purified from extracts of gastrointestinal tissues of the urodele, Amphiuma tridacrylum (three-toed amphiuma), and the elas mobranch Sphyrna lewini (hammerhead shark), and from the brain of the agnathan Lampetra fluviatilis (river lamprey). The amphiuma substance P (SP) (DNPSVGQFYGLM-NH2) contains 12 amino residues compared with 11 for mammalian SP and lacks the Arg/Lys-Pro-Xaa-Pro motif that is chara cteristic of NK, receptor-selective agonists. Lampetra SP (RKPHPKEFVGL M-NH2) is identical to SP from the sea lamprey and the shark SP-relate d peptide (AKFDKFYGLM-NH2) is identical to dogfish scyliorhinin L. Amp hiuma neurokinin A (NKA) (HKDAFIGLM-NH2) and lamprey NKA (HFDEFVGLM-NH 2) contain 9 amino acid residues compared with 10 for mammalian NKA. T he shark NKA-related peptide (ASGPTQAGIV(10)GRKRQKGEMF(20)VGLM-NH2) sh ows limited structural similarity to mammalian neuropeptide gamma and the teleost tachykinin, carassin but contains 24 rather than 21 amino acid residues. The data show that the primary structures of the tachyk inins have been very poorly conserved during vertebrate evolution and that pressure has acted only to maintain the functionally important se quence -Phe-Xaa-Gly- Leu-Met-NH2 at the COOH-termini of the peptides.