Bradykinin (1-5), a major stable metabolite of Bradykinin, is formed by the proteolytic action of angiotensin-converting enzyme (ACE). The bradykinin (BK) fragment (1-5) (RPPGF) is one of the most stable naturally occurring metabolites.
Bradykinin (1-6) is an amino-truncated Bradykinin peptide and a stable metabolite of Bradykinin, cleaved by carboxypeptidase Y (CPY). This fragment of Bradykinin activates pain receptors and induces smooth muscle contraction.