Kallikrein generates angiotensin II but not bradykinin in the plasma of the urodele, Amphiuma tridactylum

Incubation of heat-denatured plasma from the urodele, Amphiuma tridactylum (three-toed amphiuma) or from the anurans Rana ridibunda (European green frog) and Rana catesbeiana (American bullfrog) with either glass beads, porcine pancreatic kallikrein or trypsin did not generate bradykinin-like immunoreactivity. However, peptides were generated in kallikrein-treated amphiuma plasma that contracted vascular rings from the bullfrog systemic arch and had a spasmogenic action on the bullfrog urinary bladder. These peptides, which were not generated in trypsin-treated plasma, were purified to homogeneity by reverse-phase HPLC and their primary structures established as: Asp-Arg-Val-Tyr-Val-His-Pro-Phe ([Asp¹,Val⁵]angiotensin II) and Asn-Arg-Val-Tyr-Val-His-Pro-Phe ([Asn¹,Val⁵]angiotensin II). Incubation of synthetic [Asn¹,Val⁵]angiotensin II with amphiuma plasma resulted in deamidation to [Asp¹,Val⁵]angiotensin II. The data suggest, therefore, that amphiuma plasma contains an l-asparagine amidohydrolase (asparaginase), as previously described for the eel. Although bradykinin-related peptides have been isolated from frog skin, this study provides evidence that the kallikrein-kinin system may be absent from the blood of amphibia.