The Kallikrein-Kinin System: A Functional Role of Plasma Kallikrein and Kininogen in Blood Coagulation

Abstract

Bradykinin is a nonapeptide with potent pharmacological activities such as smooth muscle contraction and hypotension. In mammalian plasma, this physiologically active peptide is in precursor form, called kininogen, and liberated by the action of specific enzyme, plasma kallikrein, or tissue kallikreins. Bovine plasma contains at least two kininogens, named high molecular weight (HMW) kininogen and low molecular weight (LMW) kininogen (Yano et al., 1967). In Figure 1, the linear polypeptide sequences of kininogens are shown for comparison. The areas of which amino acid sequence has been established are indicated by shaded areas. HMW kininogen consists of a single chain with a molecular weight of 76,000, containing four segments, heavy chain, the kinin moiety, fragment 1·2 and light chain (Han et al., 1976). It contains 580 amino acid residues and 12.5% carbohydrates. This kininogen is the physiological substrate of plasma kallikrein (Yano et al., 1971). LMW kininogen, on the other hand, has a molecular weight of 48,000. It consists of 380 residues and 16.4% carbohydrate (Kato et al., 1976).