Bradykinin-related peptide family

General Bradykinin, a 9 amino-acid peptide, is a potent endothelium-dependent vasodilator that causes contraction of non-vascular smooth muscle, increases vascular permeability and is involved in the mechanism of pain. Bradykinin also causes natriuresis, contributing to a drop in blood pressure.

Synthesis
Bradykinin is proteolytically cleaved from its kininogen precursor by the enzyme kallikrein.

Metabolism
Bradykinin is broken down by three kininases: angiotensin-converting enzyme (ACE) , aminopeptidase P (APP), and carboxypeptidase N (CPN), which cleave the 7-8, 1-2, and 8-9 positions, respectively.

Receptors
Bradykinin has two receptors, the bradykinin B1 and B2 receptors that belong to G protein coupled receptor (GPCR) family. The B1 receptor is expressed only as a result of tissue injury, and is presumed to play a role in chronic pain. This receptor has been also described to play a role in inflammation. The B2 receptor is constitutively expressed and participates in bradykinin's vasodilatory role.

Bradykinin-related peptides in venom
Several bradykinin-related peptides have been described in spider and insect venoms (see the right box), as well as in amphibian skin secretions (see proteins here.

Liberation of endogenous bradykinin by venom serine proteases Endogenous bradykinin can also be generated by the action of venom serine proteases (see proteins with this action here, and the serine protease description file here).