Biological activity of synthetic polypeptides with bradykinin-like properties

The biological activity of synthetic polypeptides containing the amino acids of natural pure trypsin-bradykinin and snake-venom-bradykinin has been investigated. A series of tests for bradykinin-like activity in stimulating plain muscle, depressing the blood pressure and increasing capillary permeability was used on various species. A nonapeptide with the following structure: H-L-Arg-L-Pro-L-Pro-Gly-L-Phe-L-Ser-L-Pro-L-Phe-L-Arg-OH elicited qualitatively and quantitatively the effects of the pure natural bradykinins. An octapeptide with the following structure: H-L-Arg-L-Pro-Gly-L-Phe-L-Ser-L-Pro-L-Phe-L-Arg-OH also exerted bradykinin-like effects but was 50 to 100 times less active than the nonapeptide. Three other octapeptides and a heptapeptide were without any significant effect. Further work will demonstrate if the nonapeptide A is synthetic bradykinin or a peptide with bradykinin-like activity.NOTE ADDED SINCE SUBMISSION OF THIS PAPER: The data from this investigation were personally precommunicated to Elliott, Lewis, and Horton, who have since found that the structure of pure trypsin-bradykinin is identical with the structure of the nonapeptide A. Therefore, this synthetic nonapeptide is in fact synthetic bradykinin.