The Kinin System of Human Plasma

Abstract

SummaryHuman plasma was adsorbed to celite. The celite eluates were chromatographed on QAE-Sephadex A-50, followed by gel filtration, isoelectric focusing and preparative polyacrylamide electrophoresis.By anion-exchange chromatography, factor XI a, kallikrein and y-globulin were isolated from the excluded protein peak. Factor XIa (MW ∼170,000) corrected the deficiency in plasmas deficient in factors XII or XI, but had no effect on the kininsystem. Its isoelectric point was about 8.0-8.5. Kallikrein had a molecular weight of ∼ 90,000 and a pi of 7.8-8.0 The two substances could be isolated also by polyacrylamide electrophoresis.Highly anionic fractions contained a fragment of factor XII a (prekallikrein activator), which activated prekallikrein and retained some of the clot-promoting property of the intact factor XIIa molecule. Its molecular weight was about 37,000, the pi about 4.4 and it migrated as a prealbumin by disc electrophoresis.It is concluded that, by massive contact exposure, most of factor XII a converts to the highly anionic, low-molecular-weight prekallikrein activator. Since the prekallikrein activator is a fragment of factor XII a, we recommend that it be referred to as “XII f”.

Isolation of prekallikrein activator from guinea pig serum or plasma adsorbed to immune precipitates or celite: Possible relationship to Hageman factor

“…It seems that, following exposure t o immune precipitates, but particularly celite, most of factor XIIa appears as an anionic fragmen t , which, although acquiring pre kallikrein-ac t iva ting activity, still retains some clot-promoting activity, which corrects the clotting defect in factor Xll-deficient plasma, but not that of plasmas deficient in other clotting factors. The clot-promoting activity and PKA-activity is similar to material obtained under similar conditions from human plasma, where we have proposed t o designate the fragment derived from XlIa as "Xllf" [25]. The acquisition of PKA-activity is paralleled by a loss of clot-promoting activity, as will be described in a succeeding paper and represents circumstantial evidence that factor XIIa is converted t o XIIf or PKA.…”

“…also been found in celite eluates (with similar properties) of human plasma [25], it is believed t o represent a fragment of plasma kallikrein.…”

Plasma Inhibitors of The Hageman Factor Dependent Pathways

“…Regulation of this system, as is the case with the other pathways, has been primarily examined by interacting the highly purified components of the system with isolated plasma inhibitors. A critical control protein operative at the common initiating step for all three Hageman factor dependent pathways is the inhibitor of the activated first component of complement, Cl inhibitor (Cī INH), which has now been isolated from human plasma in highly purified form by several methods [18,38,47]. It appears to be a heat and acid labile alpha-2 globulin which reacts rapidly and stoichiometrically with the activated first component of complement CL Studies by Pensky and Schwick [40] suggest immunochemical similarity if not identity with an alpha-2 neuraminoglycoprotein of human plasma.…”

“…Forbes, Pensky and Ratnoff originally demonstrated the capacity of Cī INH to inhibit the action of activated Hageman factor in clotting assays [6]. Studies have also revealed that partially purified Cī INH suppresses the esterase activity of the 37,000 molecular weight Hageman factor fragment on benzoyl arginine ethyl ester [38] and is effective in inhibiting activated Hageman factor or the Hageman factor fragments' capacity to generate plasminogen activator from plasminogen proactivator in a system utilizing purified components [47]. Inhibition by Cī INH was achieved in a dose dependent fashion.…”

“…The first plasma inhibitor observed to play a role in regulating the kinin forming pathway was Cl INH. As mentioned above, Cl INH was shown by Forbes et al to inhibit the coagulant activity of activated Hageman factor [6] and by Ozge-Anwar et al to inhibit the esterase activity of the Hageman factor fragments [38]. In addition, Cl INH has been shown to inhibit the capacity of Hageman factor or its fragments to activate prekallikrein to kallikrein [47].…”