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

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Abstract
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 acetone 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 chemically sequenced, and its molecular weight was determined by fast atom bombardment mass spectrometry (FABms). The peptide is 22 amino acids long and has considerable sequence similarity to the known natriuretic peptides, especially within the disulfide bonded "ring"; but unlike these known peptides it ends immediately after the second half cystine. Though it lacks a C-terminal "tail," the killfish peptide is equipotent to rat ANP in our radioimmunoassay, which employs an antiserum 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.

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