Kininogens are inhibitors of thiol proteases. HMW-kininogen plays an important role in blood coagulation by helping to position optimally prekallikrein and factor XI next to factor XII; HMW-kininogen inhibits the thrombin- and plasmin-induced aggregation of thrombocytes. LMW-kininogen inhibits the aggregation of thrombocytes. LMW-kininogen is in contrast to HMW-kininogen not involved in blood clotting.
The active peptide bradykinin is a potent vasodilatator that is released from HMW-kininogen shows a variety of physiological effects: (A) influence in smooth muscle contraction, (B) induction of hypotension, (C) natriuresis and diuresis, (D) decrease in blood glucose level, (E) it is a mediator of inflammation and causes (E1) increase in vascular permeability, (E2) stimulation of nociceptors (4E3) release of other mediators of inflammation (e.g. prostaglandins), (F) it has a cardioprotective effect (directly via bradykinin action, indirectly via endothelium-derived relaxing factor action).
Subcellular locations: Secreted, Extracellular space
Secreted in plasma. T-kinin is detected in malignant ovarian, colon and breast carcinomas, but not in benign tumors.