Mass spectrometric study of bradykinin-related peptides (BRPs) from the skin secretion of Russian ranid frogs.

Amphibian skin secretion is known to contain biologically active peptides. Bradykinins and related peptides (BRPs) can be found in these animals, while frogs from the genus Rana are considered to be leaders in the levels and variety of these peptides. A reasonable rationalization of this fact is that bradykinins are efficient defense compounds against predators. Forty-four various BRPs have been identified in the skin secretions of five ranid frog species (R. ridibunda, R. lessonae, R. esculenta, R. temporaria, R. arvalis) from the Zvenigorod region (Moscow district, Russia). Some of these peptides are already known, but the novel ones constitute a significant portion. An interesting group of novel peptides was isolated from R. lessonae. These are bradykinin analogues bearing a tyrosine residue in the 5th or 8th position. [Arg(0), Trp(5), Leu(8)]bradykinin and [Thr(6), Leu(8)]bradykinin that had been isolated from fish and avian species, respectively, were also detected in the frog secretion, supporting the predator defense hypothesis. Furthermore, a novel group of BRPs named 'lessonakinins' was discovered in R. lessonae and R. esculenta. All of them include the [Arg(0), Trp(5), Leu(8)]bradykinin sequence and have some structural resemblance to the precursor of this peptide cloned by Chen and coworkers recently. However, the C-terminal part of the lessonakinins does not match the sequence predicted by Chen, demonstrating possible incompleteness of information obtained by cDNA cloning.