The Sequencing, Synthesis, and Biological Actions of an ANP-Like Peptide Isolated from the Brain of the Killifish Fundulus heteroclitus

We have extracted, purified, and sequenced an ANP-like peptide from the killifish. The peptide was extracted from whole brains with acidic acetone, and the aqueous phase remaining after evaporation of the ace- tone was subjected directly to HPLC. A pure peak was obtained after three successive HPLC steps. A key part of our purification method was the deliberate oxidation of methionyl residues in the peptide between the second and third HPLC steps. The purified peptide was chemi- cally sequenced, and its molecular weight was deter- mined by fast atom bombardment mass spectrometry (FABms). The peptide is 22 amino acids long and has considerable sequence similarity to the known natri- uretic peptides, especially within the disulfide bonded "ring"; but unlike these known peptides it ends immedi- ately after the second half cystine. Though it lacks a C- terminal "tail," the killifish peptide is equipotent to rat ANP in our radioimmunoassay, which employs an anti- serum to the rat peptide. Furthermore, this brain peptide is equipotent to eel ANP in relaxing toadfish aortic rings, though both fish peptides are slightly less potent than rat ANP.