Purification, structural characterization, and myotropic activity of endothelin from trout, Oncorhynchus mykiss

Endothelin (ET) from a nontetrapod species has never been characterized, ei ther structurally or biologically. A single molecular form of trout ET with al-amino-acid residues was isolated in pure form from an extract of the ki dney of the steelhead trout, Oncorhynchus mykiss and its primary structure established as Cys-Ser-Cys-Ala-Thr-Phe-Leu-Asp-Lys-Glu(10)-Cys-Val-Tyr-Phe- Cys-His-Leu-Asp-Ile-Ile(20)-Trp. This amino acid sequence shows only three substitutions (Ala(4)-->Ser, Thr(5)-->Ser, and Phe(6)-->Trp) compared with human ET-2, demonstrating that the structure of the peptide has been well c onserved during evolution and that the pathway of posttranslational process ing of preproendothelin in the trout is probably similar to that in mammals . Synthetic trout ET produced concentration-dependent constrictions of isol ated rings of vascular tissue from trout efferent branchial artery (EBA; pD (2) = 7.90 +/- 0.06, n = 5), caeliacomesenteric artery (pD(2) = 8.03 +/- 0. 04, n = 4), anterior cardinal vein (ACV; pD(2) = 8.57 +/- 0.25, n = 4), and rat abdominal aorta (AO; pD(2) = 8.86 +/- 0.08, n = 7). Trout and rat vess els were more sensitive to mammalian ET-1 than to trout ET (pD(2) for human ET-1 in: EBA = 9.12 +/- 0.14; ACV = 9.90 +/- 0.15; AO = 8.86 +/- 0.08), bu t there was no significant difference in the maximum tension produced by ei ther peptide in these vessels.