TETRAPOD-TYPE ASP1 ANGIOTENSIN IS PRESENT IN A HOLOSTEAN FISH, AMIA CALVA

Abstract The renin-angiotensin system has been identified in various vertebrates, from elasmobranchs to mammals. Tetrapod (amphibians to mammals) angiotensin (ANG) has Asp at the N-terminus, but Asp is replaced by Asn in elasmobranch and teleost fish. ANG I has been isolated from incubates of plasma and kidney extracts of the bowfin Amia calva, a holostean fish, using the eel vasopressor activity as an assay system; its sequence was found to be H-Asp-Arg-Val-Tyr-Val-His-Pro-Phe-Asn-Leu-OH after sequence analysis, mass spectrometry, and comparison with the synthetic peptide. This sequence is identical to bullfrog ANG I. [Asn 1 ] ANG I was not detected. Thus the bowfin is the first fish species which contains only [Asp 1 ] ANG I. The bowfin ANG I and II were no more vasopressor than eel peptides in the bowfin, indicating that bowfin ANG II receptors do not distinguish between [Asp 1 ] and [Asn 1 ] peptides. In the rat, bowfin ANG I and rat [Ile 5 , His 9 ] ANG I have equipressor activities when examined in different animals, but the vasopressor activity of bowfin ANG I decreased following rat ANG I in the same animals, although the activity of rat ANG I was unaffected after bowfin ANG I. The present study directly demonstrates the presence of the renin-angiotensin system in a holostean fish and showed that its ANG II receptors have not yet fully coevolved with the homologous [Asp 1 ] peptide.