Characterization of bradykinin-related peptides generated in the plasma of six sarcopterygian species (African Lungfish, Amphiuma, Coachwhip, Bullsnake, Gila Monster, and Gray's Monitor)

Incubation of heat-denatured plasma from six species occupying different evolutionary positions within the Sarcopterygian lineage [the dipnoan, Protopterus annectens (African lungfish); the urodele, Amphiuma tridactylum (three-toed amphiuma); the colubrid snakes, Pituophis melanoleucus sayi (bullsnake) and Masticophis flagellum (coachwhip); and the lizards Heloderma suspectum (Gila monster) and Varanus Grayi (Gray's monitor)] with trypsin generated bradykinin-related peptides that were detected by radioimmunoassay using an antiserum raised against mammalian bradykinin (BK). The peptides were purified by HPLC and their primary structures were established as lungfish [Tyr¹,Gly²,Ala⁷,Pro⁸]BK, amphiurea [Phe¹,Ile²,Leu⁵]BK, bullsnake and coachwhip [Val¹,Thr⁶]BK, Gila monster [Leu²,Thr⁶]BK, and Grays monitor [Thr⁶]BK. Monitor BK is identical to the peptide generated in turtle and alligator plasma and coachwhip/bullsnake BK shows one amino acid substitution (Ala¹ → Val) compared with the peptide generated in the plasma of the python. The data provide further evidence for the widespread occurrence of a kallikrein-kininogen system in nonmammalian vertebrates but indicate that the primary structure of BK has been poorly conserved during evolution.