A serine protease that cleaves Lys-Arg and Arg-Ser bonds in kininogen to release bradykinin. Present in plasma as an inactive precursor prekallikrein, cleaved by Factor XII. Plasma kallikrein liberates kinins (bradykinin and kallidin) from the kininogens, peptides responsible for the regulation of blood pressure and activation of inflammation. It is also capable of generating plasmin from plasminogen.