After limited digestion of purified human HMW-kininogen by plasmin, the kininogen molecule consists of two disulfide-linked chains in which the bradykinin sequence resides in the "light chain" portion. Kinin was released from this molecule by plasma kallikrein at a two- to three-fold more rapid rate than from uncleaved HMW-kininogen. Similarly, when normal human plasma or prekallikrein deficient plasma was treated with sufficient streptokinase to activate plasminogen the subsequent rate of release of kinin by kallikrein was enhanced. The digestion of HMW-kininogen by plasmin as well as kinin relea^s was inhibited by epsilon aminocaproic acid at a concentration of 10−3 M, suggesting that one or more lysine residues was critical to the plasmin-HMW-kininogen interaction. Leukocyte elastase cleaved HMW-kininogen into low molecular weight fragments without releasing kinin but plasma kallikrein could then release kinin from a low molecular weight component of elastase-digested HMW-kininogen (≦50 kd mol. wt.). Elastase destroyed the coagulant properties of the kininogen
When HMW-kininogen was converted to two-chain, disuifide-linked molecules, either by plasmin or kallikrein, the quantity of antigen detected in an ELISA with polyclonal antibody to human light chain antigens was significantly increased. Expression of antigen detectable with a monoclonal antibody to an epitope located close to the disulfide interchange in the light chain was not increased by prior limited digestion with these enzymes
It is possible that minimal activation of plasminogen in vivo may facilitate kinin release by kallikrein. In addition, in quantifying antigenic properties of HMW-kininogen in plasma, care should be taken to block in vitro activation of plasminogen or prekallikrein. Since leukocyte elastase can be released during clotting of whole blood, it might then serve as a regulator of coagulation through its inactivation of coagulant properties of HMW-kininogen
