Kininogen cleaved by tissue kallikrein forms kallidin (Lys-bradykinin). A portion of kininogen is hydroxylated on the third amino acid of the bradykinin sequence, proline, leading to the formation of hydroxylated kinin peptides. Hydroxylated kinins have similar biological activity as non-hydroxylated kinins. Kallidin is one of the main kinins in mammals. It acts as an agonist for the type 2 (B2) bradykinin receptor and is a potent inflammatory mediator produced during acute and chronic inflammation.