Human plasma prekallikrein: a rapid high-yield method for purification

Kallikrein and kallikrein-like proteinases: purification and determination by chromatographic and electrophoretic methods

Kallikreins and kallikrein-like enzymes make up a family of serine proteinases present in tissues and body fluids of mammals and in some snake venoms. This review deals with the procedures of purification, detection and determination of these enzymes by chromatographic and electrophoretic methods. The procedures are reported in tables, described and discussed with the aim of illustrating the state-of-the-art of research in the field.

Endothelial cells produce a substance that inhibits contact activation of coagulation by blocking the activation of Hageman factor

Human umbilical vein endothelial cells (HUVECs) produce a property that impairs the generation of coagulant and amidolytic activity initiated when normal human plasma is exposed to glass. This inhibitory property blocks the adsorption of Hageman factor (factor XII) to glass, thereby preventing the activation of Hageman factor, but does not impair the coagulant or amidolytic activity of already activated Hageman factor (factor XIIa). This property in HUVEC lysates could be neutralized by a purified preparation of Hageman factor but not by purified prekallikrein or high molecular mass kininogen. A partially purified inhibitory fraction from cell lysates exhibited a single homogeneous band in SDS/PAGE of approximately 22.5 kDa. Inhibitory activity was also found in concentrates of conditioned media from HUVECs, which also impaired the binding of Hageman factor to a surface; it may not be identical with that found in cell lysates.

Kinetics of inhibition of platelet calpain II by human kininogens

The plasma kininogens, high-molecular-mass and low-molecular-mass kininogens, are the most potent plasma inhibitors of platelet calpain. We explored the kinetic mechanisms for kininogen inhibition of calpain by comparing calpain inactivation by human high-molecular-mass kininogen (HK) and human low-molecular-mass kininogen (LK). With a [14C]methylated alpha-casein substrate, the inhibition of calpain by HK did not follow classic Michaelis-Menten kinetics. With the use of a fluorogenic assay with the dipeptide substrate for calpain, 3-carboxypropionyl-leucyltyrosine 7-(4-methyl)coumarylamide, the inhibition by HK and LK fitted a kinetic model of tight-binding inhibition. LK was found to be a non-competitive inhibitor of platelet calpain with a Ki of 2.7 nM. HK showed mixed non-competitive inhibition of calpain with a Ki of 2.3 nM in the absence of substrate and Ki of 0.71 nM in the presence of saturating substrate, almost 4-fold tighter than LK. Proteolysis of HK by plasma and tissue kallikreins did not influence its ability to inhibit calpain. Digestion of the HK light chain by Factor XIa also did not alter its calpain-inhibitory function. These studies indicate that the kininogens are tight-binding non-competitive inhibitors of platelet calpain, the inhibitory domain in each case being mainly on the heavy chain. The light chain of HK appears to influence its kinetic behaviour.

Studies on the human plasma kallikrein-kinin system: alpha-kallikrein does not directly activate blood neutrophils

alpha-Kallikrein was prepared using an improved purification protocol (Burger, D., Schleuning, W.-D. and Schapira, M. (1986) J. Biol. Chem. 261, 324-327) and was employed to reevaluate our previous observations indicating that kallikrein activates blood neutrophils by a mechanism requiring an uncleaved Mr 52,000 NH2-terminal heavy chain. Cellular activation was evaluated by measuring neutrophil aggregation, release of both vitamin B12 binding capacity and myeloperoxidase, and generation of superoxide anion. Whereas all these indicators were evoked by exposing neutrophils to f-Met-Leu-Phe, phorbol myristate acetate, zymosan activated serum, or the calcium ionophore A 23187, we show here that neutrophils incubated with alpha-kallikrein remained unactivated. Moreover, we demonstrate that this lack of activation is accompanied by an inability of neutrophils to specifically bind alpha-kallikrein.

Effect of negatively charged activating compounds on inactivation of factor XIIa by Cl inhibitor

Human factor XII, upon exposure to negatively charged surfaces such as kaolin, sulfatides, and heparin, is converted to enzymatic forms, factor XIIa and factor XIIf. Cl inhibitor has been quantitatively demonstrated to be the primary plasma inhibitor of both factor XIIa and factor XIIf. Studies were performed to determine whether the presence of artificial, negatively charged surfaces influenced the ability of Cl inhibitor to inhibit factors XIIa and XIIf. Kaolin and sulfatides slowed the rate of inhibition of factor XIIa by Cl inhibitor 4.8- and 2-fold, respectively, whereas they had no effect on the inhibition of factor XIIf by Cl inhibitor. Heparin in a concentration of 65 U/ml decreased the inhibition rate of factor XIIa by Cl inhibitor, but, at the same concentration, had less of an effect on the ability of Cl inhibitor to inhibit factor XIIf. These studies indicate that negatively charged surfaces protect factor XIIa but not factor XIIf from inhibition from Cl inhibitor. Since the difference between factors XIIa and XIIf consists of the presence of a surface binding region in factor XIIa, the basis of this protection must reside in the surface binding residues of factor XII. These in vitro events suggest that surface-bound factor XIIa may hydrolyze its physiologic substrates, factor XI and prekallikrein, in an environment partially protected from inhibition by Cl inhibitor.

Recent evolutionary divergence of plasma prekallikrein and factor XI

The evolution in mammals of the zymogens of the contact activation system of coagulation (factor XII, prekallikrein and factor XI) has been investigated. The NH2-terminal sequences of human plasma prekallikrein and the heavy and light chains of kallikrein have been determined and compared with those of bovine prekallikrein and of human and bovine factors XII and XI. The human and bovine NH2-terminal sequences of the light chains (catalytic polypeptide) show striking similarities both among themselves and with those of the catalytic polypeptide chains of other coagulation and digestive proteases, indicating a common origin. Comparison of the NH2-terminal sequences of human prekallikrein with those of the bovine prekallikrein and human bovine factors XIa and XIIa indicates a common origin of the heavy chain of kallikrein and factor XIa, different from that of either factor XIIa or other known amino acid sequences. Ancestral sequences for human and bovine prekallikrein and factor XI, deduced by genetic analysis of the minimum number of base changes indicate that the NH2-terminus of prekallikrein and factor XI have evolved at about the same rate. The estimated time for the gene duplication was about 124 million years ago, a value consistent with the age of the mammals.

High molecular weight kininogen binds to unstimulated platelets

Studies were performed to determine if the unstimulated platelet membrane has a site for high molecular weight kininogen (HMWK) binding. 125I-HMWK bound to unstimulated platelets. Zn++ was required for 125I-HMWK binding to unstimulated platelets and binding was maximal at 50 microM Zn++. Neither Mg++ nor Ca++ substituted for Zn++ in supporting 125I-HMWK binding to unstimulated platelets, and neither ion potentiated binding in the presence of 50 microM zinc. 125I-HMWK competed with equal affinity with HMWK for binding, and excess HMWK inhibited 125I-HMWK-platelet binding. Only HMWK, not prekallikrein, Factor XII, Factor XI, Factor V, fibrinogen, or fibronectin inhibited 125I-HMWK-platelet binding. 125I-HMWK binding to unstimulated platelets was 89% reversible within 10 min with a 50-fold molar excess of HMWK. Unstimulated platelets contained a single set of saturable, high affinity binding sites for 125I-HMWK with an apparent dissociation constant of 0.99 nM +/- 0.35 and 3,313 molecules/platelet +/- 843. These studies indicate that the unstimulated external platelet membrane has a binding site for HMWK that could serve as a surface to modulate contact phase activation.

Alpha-1-antitrypsin-Pittsburgh. A potent inhibitor of human plasma factor XIa, kallikrein, and factor XIIf

Alpha-1-antitrypsin-Pittsburgh is a human variant that resulted from a point mutation in the plasma protease inhibitor, alpha 1-antitrypsin (358 Met----Arg). This defect in the alpha 1-antitrypsin molecule causes it to have greatly diminished anti-elastase activity but markedly increased antithrombin activity. In this report, we demonstrate that this variant protein also has greatly increased inhibitory activity towards the arginine-specific enzymes of the contact system of plasma proteolysis (Factor XIa, kallikrein, and Factor XIIf), in contrast to normal alpha 1-antitrypsin, which has modest to no inhibitory activity towards these enzymes. We determined the second-order-inactivation rate constant (k'') of purified, human Factor XIa by purified alpha 1-antitrypsin-Pittsburgh and found it to be 5.1 X 10(5) M-1 s-1 (23 degrees C), which is a 7,700-fold increase over the k'' for Factor XIa by its major inhibitor, normal purified alpha 1-antitrypsin (i.e., 6.6 X 10(1) M-1 s-1). Human plasma kallikrein, which is poorly inhibited by alpha 1-antitrypsin (k'' = 4.2 M-1 s-1), exhibited a k'' for alpha 1-antitrypsin-Pittsburgh of 8.9 X 10(4) M-1 s-1 (a 21,000-fold increase), making it a more efficient inhibitor than either of the naturally occurring major inhibitors of kallikrein (C-1-inhibitor and alpha 2-macroglobulin). Factor XIIf, which is not inhibited by normal alpha 1-antitrypsin, displayed a k'' for alpha 1-antitrypsin-Pittsburgh of 2.5 X 10(4) M-1 s-1. This enhanced inhibitory activity is similar to the effect of alpha 1-antitrypsin-Pittsburgh that has been reported for thrombin. In addition to its potential as an anticoagulant, this recently cloned protein may prove to be clinically valuable in the management of septic shock, hereditary angioedema, or other syndromes involving activation of the surface-mediated plasma proteolytic system.

The contact activation system: biochemistry and interactions of these surface-mediated defense reactions

This review is intended to be a critical state-of-the-art overview of the activation and inhibition of the proteins (factor XII, prekallikrein, high molecular weight kininogen, and factor XI) of the contact phase of coagulation. Specifically, this review will reconsider the concept of the reciprocal activation of the proteases of the contact phase of coagulation, factor XII, and prekallikrein, in light of much recent evidence indicating that factor XII, itself, autoactivates when associated with negatively charged surfaces. In addition, the mechanisms for amplification of activation of the proteins of the contact phase of coagulation will be discussed from the pivotal role of high molecular weight kininogen, or one of its altered forms, serving as a cofactor to order the activation of the zymogens it is associated with. The role and relative importance of each of the naturally occurring plasma protease inhibitors (C1-inhibitor, alpha-2-macroglobulin, alpha-1-antitrypsin, antithrombin III, and alpha-1-antiplasmin) will be assessed as they relate to the dampening of contact phase activation. Finally, the contact phase of coagulation activation will be discussed not only as a plasma proteolytic mechanism, but also as it interacts with platelets.

Human plasma kallikrein and C1 inhibitor form a complex possessing an epitope that is not detectable on the parent molecules: demonstration using a monoclonal antibody

The inactivation of human plasma kallikrein (EC 3.4.21.8) by the inhibitor of activated complement component 1 (C1 inhibitor) induces the formation of a 1:1 stoichiometric kallikrein-C1 inhibitor complex and a proteolytically modified form of C1 inhibitor. We have produced a monoclonal antibody that recognizes the kallikrein-C1 inhibitor complex as well as modified C1 inhibitor but fails to react with virgin C1 inhibitor or native plasma kallikrein. This observation constitutes an unequivocal demonstration that the reaction between plasma kallikrein and C1 inhibitor leads to the emergence of an epitope that is undetectable on the parent enzyme and inhibitor molecules.

Inactivation of factor XII active fragment in normal plasma. Predominant role of C-1-inhibitor

To define the factors responsible for the inactivation of the active fragment derived from Factor XII (Factor XIIf ) in plasma, we studied the inactivation kinetics of Factor XIIf in various purified and plasma mixtures. We also analyzed the formation of 125I-Factor XIIf -inhibitor complexes by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). In purified systems, the bimolecular rate constants for the reactions of Factor XIIf with C-1-inhibitor, alpha 2-antiplasmin, and antithrombin III were 18.5, 0.91, and 0.32 X 10(4) M-1 min-1, respectively. Furthermore, SDS-PAGE analysis revealed that 1:1 stoichiometric complexes were formed between 125I-Factor XIIf and each of these three inhibitors. In contrast, kinetic and SDS-PAGE studies indicated that Factor XIIf did not react with alpha 1-antitrypsin or alpha 2-macroglobulin. The inactivation rate constant of Factor XIIf by prekallikrein-deficient plasma was 14.4 X 10(-2) min-1, a value that was essentially identical to the value predicted from the studies in purified systems (15.5 X 10(-2) min-1). This constant was reduced to 1.8 X 10(-2) min-1 when Factor XIIf was inactivated by prekallikrein-deficient plasma that had been immunodepleted (less than 5%) of C-1-inhibitor. In addition, after inactivation in normal plasma, 74% of the active 125I-Factor XIIf was found to form a complex with C-1-inhibitor, whereas 26% of the enzyme formed complexes with alpha 2-antiplasmin and antithrombin III. Furthermore, 42% of the labeled enzyme was still complexed with C-1-inhibitor when 125I-Factor XII was inactivated in hereditary angioedema plasma that contained 32% of functional C-1-inhibitor. This study quantitatively demonstrates the dominant role of C-1-inhibitor in the inactivation of Factor XIIf in the plasma milieu.

Cleavage of human high molecular weight kininogen markedly enhances its coagulant activity. Evidence that this molecule exists as a procofactor

High molecular weight kininogen (HMW)-kininogen, the cofactor of contact-activated blood coagulation, accelerates the activation of Factor XII, prekallikrein, and Factor XI on a negatively charged surface. Although prekallikrein and Factor XI circulate as a complex with HMW-kininogen, no physical association has been demonstrated between Factor XII and HMW-kininogen, nor has the order of adsorption to surfaces of these proteins been fully clarified. In this report we explore the requirements for adsorption of HMW-kininogen to a clot-promoting surface (kaolin), in purified systems, as well as in normal plasma and plasma genetically deficient in each of the proteins of the contact system. The fraction of each coagulant protein associated with the kaolin pellet was determined by measuring the difference in coagulant activity between the initial sample and supernatants after incubation with kaolin, or by directly quantifying the amount of 125I-HMW-kininogen that was associated with the kaolin pellet. In normal plasma, the adsorption of HMW-kininogen to kaolin increased as the quantity of kaolin was increased in the incubation mixture. However, the HMW-kininogen in Factor XII-deficient plasma did not absorb appreciably to kaolin. Furthermore, the quantity of HMW-kininogen from prekallikrein-deficient plasma that adsorbed to kaolin was decreased as compared with normal plasma. These observations suggested that HMW-kininogen in plasma must be altered by a reaction involving both Factor XII and prekallikrein in order for HMW-kininogen to adsorb to kaolin, and to express its coagulant activity. Subsequently, the consequence of the inability of HMW-kininogen to associate with a negatively charged surface results in decreased surface activation. This assessment was derived from the further observation of the lack of prekallikrein adsorption and the diminished Factor XI adsorption in both Factor XII-deficient and HMW-kininogen-deficient plasmas, since these two zymogens (prekallikrein and Factor XI) are transported to a negatively charged surface in complex with HMW-kininogen. The percentage of HMW-kininogen coagulant activity that adsorbed to kaolin closely correlated (r = 0.98, slope = 0.97) with the amount of 125I-HMW-kininogen adsorbed, suggesting that adsorption of HMW-kininogen results in the expression of its coagulant activity. Since kallikrein, which is known to cleave HMW-kininogen, is generated when kaolin is added to plasma, we tested the hypothesis that proteolysis by kallikrein was responsible for the enhanced adsorption of HMW-kininogen to kaolin. When purified HMW-kininogen was incubated with purified kallikrein, its ability to absorb to kaolin increased with time of digestion until a maximum was reached. Moreover, (125)I-HMW-kininogen, after cleavage by kallikrein, had markedly increased affinity for kaolin than the uncleaved starting material. Furthermore, fibrinogen, at plasma concentration (3 mg/ml), markedly curtailed the adsorption of a mixture of cleaved and uncleaved HMW-kininogen to kaolin, but was unable to prevent fully cleaved HMW-kininogen from adsorbing to the kaolin. Addition of purified kallikrein to Factor XII-deficient plasma, which bypasses Factor XII-dependent contact-activation amplified the ability of its HMW-kininogen to adsorb to kaolin. These observations indicate that HMW-kininogen is a procofactor that is activated by kallikrein, a product of a reaction which it accelerates. This cleavage, which enhances its association with a clot-promoting surface in a plasma environment, is an event that is necessary for expression of its cofactor activity. These interactions would allow coordination of HMW-kininogen adsorption with the adsorption of Factor XII, which adsorbs independently of cleavage, to the same negatively charged surface.

Plasma prorenin in humans and dogs. Species differences and further evidence of a systemic activation cascade

We have studied the dog as a potential model for the human plasma prorenin-renin system. On a regular sodium intake, healthy conscious dogs apparently have a much lower plasma renin activity (PRA) than healthy human volunteers. Cryoactivation of prorenin is virtually absent in dogs, in contrast to that in humans, but becomes more effective after preacidification of the plasma. The concentration of trypsin required for optimal activation of prorenin is 6 to 10 times higher for dog plasma, revealing a prorenin:renin ratio about 10 times greater than in humans. Dialysis of posttryptic plasma decreases the PRA, but it remains 5 times higher than in pretryptic plasma, indicating that activation is not totally dependent on any renin system component that has been rendered dialyzable by trypsin, e.g., substrate converted to tetradecapeptide (TDP). This argues against the view that tryptic activation is attributable to angiotensin production from TDP by the action of cathepsin D, rather than from new renin converted from prorenin. The posttryptic increase in PRA is evident whether plasma incubation is carried out at pH 6.0 or at 7.4, and can be largely blocked by pepstatin, which also implicates a prorenin-renin mechanism rather than TDP-cathepsin. The low PRA in dogs, the negligible cryoactivation and its improvement by preacidification, and the requirement and tolerance of high trypsin concentrations, all point to greater protease inhibition in dog plasma and/or departures from the enzyme(s) responsible for human prorenin activation. Moreover, the tryptic activation of prorenin is not completed quickly as in human plasma, but carries over into the posttryptic stage of angiotensin generation, even in the presence of excess soybean trypsin inhibitor (SBTI), and other potent inhibitors. Such ongoing prorenin activation cannot be attributed only to trypsin itself, nor to kallikrein (both are inhibited by SBTI), but rather to some other enzyme(s) derived by the action of trypsin. This new prorenin convertase activity (possibly renin itself) can be effectively transferred from trypsinized to control dog plasma, in which it greatly accelerates prorenin activation. Thus, contrary to other reports, dog plasma has a high content of activatable prorenin, and with appropriate methodological changes, the dog can be used as an animal model for physiological and biochemical studies of the prorenin-renin system.

Purified human plasma kallikrein aggregates human blood neutrophils

Exposure of human blood polymorphonuclear leukocytes (PMN) to purified active plasma kallikrein resulted in PMN aggregation when kallikrein was present at concentrations ranging from 0.4 to 0.6 U/ml (0.18-0.27 microM). Kallikrein-induced PMN aggregation was not mediated through C5-derived peptides, because identical responses were observed whether or not kallikrein had been preincubated with an antibody to C5. Moreover, kallikrein was specific for aggregating PMN, because no aggregation was observed with Factor XII active fragments (23 nM), Factor XIa (0.6 U/ml or 15nM), thrombin (1.6 microM), plasmin (2 microM), porcine pancreatic elastase (2 microM), bovine pancreatic chymotrypsin (2 microM), or bradykinin (1 microM). Bovine pancreatic trypsin (2 microM) aggregated PMN, but to a lesser extent than kallikrein (0.18 microM). Kallikrein was a potent aggregant agent for PMN because similar responses were observed with kallikrein (0.5 U/ml or 0.23 microM) and an optimal dose (0.2 microM) of N-formyl-methionyl-leucyl-phenylalanine. In addition, PMN incubation with kallikrein resulted in stimulation of their oxidative metabolism as assessed by an increased oxygen uptake. Neutropenia and leukostasis observed in diseases associated with activation of the contact phase system may be the result of PMN aggregation by plasma kallikrein.

Inactivation of factor XIa by plasma protease inhibitors: predominant role of alpha 1-protease inhibitor and protective effect of high molecular weight kininogen

Factor XIa is a plasma protease that, by activating Factor IX, plays an important role in the early phase of the intrinsic pathway of blood coagulation. Four plasma protease inhibitors, alpha(1)-protease inhibitor, antithrombin III, C1-inhibitor, and alpha(2)-plasmin inhibitor, have been reported to inactivate human Factor XIa, but their quantitative contribution to the inactivation of Factor XIa in plasma has not been fully assessed. Using purified systems, we observed that the second-order rate constants for the reaction of Factor XIa with alpha(1)-protease inhibitor, antithrombin III, and CI-inhibitor were 4.08, 10, and 14.6 M(-1) min(-1) x 10(3), respectively. The pseudo-first-order rate constants, at plasma concentration of the inhibitors, were 1.86 x 10(-1), 4.68 x 10(-2), and 2.4 x 10(-2) min(-1), respectively. These kinetic data predict that alpha(1)-protease inhibitor should account for 68%, antithrombin III for 16%, and C1-inhibitor and the equipotent alpha(2)-plasmin inhibitor each for 8% of the total inhibitory activity of plasma against Factor XIa. The rate of inactivation of Factor XIa in various plasma samples specifically deficient in inhibitors was consistent with these predictions. Factor XI, the zymogen form of Factor XIa, circulates in plasma associated with the contact system cofactor, high molecular weight kininogen (HMW kininogen). Kinetic analysis indicated the existence of a reversible bimolecular Factor XIa-HMW kininogen complex with a dissociation constant (K(d)) = 0.17 muM. The light chain derived from HMW kininogen decreased the inactivation rate of Factor XIa by C1-inhibitor with a K(d) of 0.08 muM for a complex of Factor XIa and the light chain derived from HMW kininogen. The protective effect of HMW kininogen was confirmed by the finding that the inactivation rate of Factor XIa in kininogen-deficient plasma was increased over normal plasma. The present study confirms that alpha(1)-protease inhibitor is the major inhibitor of Factor XIa in plasma, and that the formation of a reversible complex between Factor XIa and HMW kininogen decreases the rate of inactivation of the enzyme by its inhibitors.

Contribution of plasma protease inhibitors to the inactivation of kallikrein in plasma

Although Cl-inhibitor (Cl-INH) and alpha(2)-macroglobulin (alpha(2)M) have been reported as the major inhibitors of plasma kallikrein in normal plasma, there is little quantitative support for this conclusion. Thus, we studied the inactivation of purified kallikrein in normal plasma, as well as in plasma congenitally deficient in Cl-INH, or artificially depleted of alpha(2)M by chemical modification of the inhibitor with methylamine. Under pseudo-first-order conditions, the inactivation rate constant of kallikrein in normal plasma was 0.60 min(-1). This rate constant was reduced to 0.35, 0.30, and 0.06 min(-1), in plasma deficient respectively in Cl-INH, alpha(2)M, or both inhibitors. Thus Cl-INH (42%) and alpha(2)M (50%) were found to be the major inhibitors of kallikrein in normal plasma. Moreover all the other protease inhibitors present in normal plasma contributed only for 8% to the inactivation of the enzyme. To confirm these kinetic results, (125)I-kallikrein (M(r) 85,000) was completely inactivated by various plasma samples, and the resulting mixtures were analyzed by gel filtration on Sepharose 6B CL for the appearance of (125)I-kallikrein-inhibitor complexes. After inactivation by normal plasma, 52% of the active enzyme were found to form a complex (M(r) 370,000) with Cl-INH, while 48% formed a complex (M(r) 850,000) with alpha(2)M. After inactivation by Cl-INH-deficient plasma, >90% of the active (125)I-kallikrein was associated with alpha(2)M. A similar proportion of the label was associated with Cl-INH in plasma deficient in alpha(2)M. After inactivation by plasma deficient in both Cl-INH and alpha(2)M, (125)I-kallikrein was found to form a complex of M(r) 185,000. This latter complex, which may involve antithrombin III, alpha(1)-protease inhibitor, and/or alpha(1)-plasmin inhibitor, was not detectable in appreciable concentrations in the presence of either Cl-INH or alpha(2)M, even after the addition of heparin (2 U/ml). These observations demonstrate that Cl-INH and alpha(2)M are the only significant inhibitors of kallikrein in normal plasma confirming previous predictions based on experiments in purified systems. Moreover, in the absence of either Cl-INH or alpha(2)M, the inactivation of kallikrein becomes almost entirely dependent on the other major inhibitor.

Isolation and immunologic properties of a heterogeneous antigen with the characteristics of the heavy chain of human plasma kininogen

Kininogen antigen was purified from human plasma fraction IV by ion exchange chromatography, gel filtration and affinity chromatography with antibody specific immunoadsorbents. The immunologically pure glycoprotein had a mol. wt of approximately 60,000 and only one polypeptide chain by SDS-PAGE. An extensive charge heterogeneity by isoelectric focusing and gel filtration on polyacrylamide agarose could only in part depend on a comparatively high sialic acid content, but may be caused by differences in the carbohydrate structures sustained by lectin-binding heterogeneity on Con A-Sepharose. This antigen shares a dominating determinant with native plasma kininogens shown by complete patterns of identity in immunochemical analyses and with the monospecific antisera developed in rabbits against the heterogeneous components. The similar size, amino acid composition, low histidine content, lack of N-terminal amino acid and antigenic homogeneity fit all the so far known characteristics of the human kininogen heavy chain. Notably the antigenic determinant is resistant to degradation by activated kallikrein. This antigen with unimpaired immunologic activity may be a useful tool for preparation of antiserum for immunochemical determination of human plasma kininogen.

Protection of human plasma kallikrein from inactivation by C1 inhibitor and other protease inhibitors. The role of high molecular weight kininogen

High Mr kininogen increases the activation rate of prekallikrein by activated factor XII on a surface. The resulting serine protease, plasma kallikrein, Mr 88 000, is inhibited in plasma by C1 inhibitor, Mr 105 000. Since prekallikrein circulates in plasma with high Mr kininogen as a complex and a kallikrein-high Mr kininogen complex can be formed in purified systems, we studied whether the inhibition of kallikrein by C1 inhibitor was influenced by high Mr kininogen. With C1 inhibitor in excess, the inactivation of kallikrein followed pseudo-first-order kinetics. The second-order rate constant for the reaction was 1.7 X 10(4) M-1 s-1, and a kallikrein-C1 inhibitor complex, Mr 190 000 was identified on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Kallikrein and C1 inhibitor formed an irreversible complex without measurable prior equilibrium. The rate of this reaction was decreased by 50% in the presence of high Mr kininogen (1 unit/mL or 0.73 muM). Kinetic analysis indicated that this protection was the result of the formation of a reversible complex between kallikrein and high Mr kininogen, which had a dissociation constant of 0.75 muM. However, low Mr kininogen did not protect kallikrein from inactivation by C1 inhibitor. High Mr kininogen also protected kallikrein from inactivation by diisopropyl fluorophosphate. These findings suggest that the kallikrein-high Mr kininogen complex was formed by noncovalent interactions between the light chains of both kallikrein and high Mr kininogen.

Human plasma kallikrein. A rapid purification method with high yield

A simple method for isolation of kallikrein from human plasma is described. Before activation of the enzyme with acetone, the plasma was treated with 0.2 M-methylamine at pH 8.2 to inactivate alpha 2-macroglobulin and thus prevent the irreversible binding of the active enzyme to the inhibitor. The enzyme was adsorbed on soya-bean trypsin inhibitor-Sepharose 4B and eluted with 5 mM-NaOH, pH 11.3. It was further purified by immunoadsorption of contaminating proteins, and gel chromatography on Ultrogel AcA 44. About 3 mg of kallikrein was obtained from 400 ml of plasma (35% yield). The purified enzyme was shown to be homogeneous by electrophoretic and immunological criteria. The specific activities against benzyloxycarbonylphenylalanylarginine methylcoumarylamide, prolylphenylalanylarginine methylcoumarylamide and tosylarginine methyl ester were higher than any previously reported. The purified enzyme was resolved into two forms of mol.wts. 88 000 and 86 000 in sodium dodecyl sulphate/polyacrylamide-gel electrophoresis without reduction. Each consisted of three chains linked by disulphide bonds, one containing the reactive serine residue (mol.wt. 36 000 or 34 000), and two additional chains (mol.wt. 28 000 and 22 000).

Function and immunochemistry of prekallikrein-high molecular weight kininogen complex in plasma

Plasma from individuals with high molecular weight (HMW) kininogen deficiency has been reported to be deficient in prekallikrein as measured by radial immunodiffusion, prekallikrein coagulant activity, and/or kaolin-activated arginine esterase activity. The discovery that prekallikrein and HMW kininogen circulate as a complex in plasma led us to reevaluate the antigenic and functional properties of prekallikrein in HMW kininogen-deficient plasma as well as in normal plasma. The low prekallikrein antigen level in an individual with HMW kininogen deficiency was corrected to the normal range (80-95%) by the addition of 0.2 U/ml of purified HMW kininogen. A similar increase in apparent prekallikrein antigen was observed when purified prekallikrein and HMW kininogen were combined. The correction of the apparent prekallikrein defect in this HMW kininogen-deficient plasma coincided with the formation of a prekallikrein-HMW kininogen complex as demonstrated by immunoelectrophoresis. Similar findings were demonstrated with purified prekallikrein and HMW kininogen by immunoelectrophoresis as well as crossed immunoelectrophoresis. The coagulant activity in HMW kininogen-deficient plasma was increased in a dose-dependent manner by the addition of HMW kininogen, reaching 85% of normal level at a concentration of 0.2 U/ml. Kaolin-activated arginine esterase activity (kallikrein) in HMW kininogen-deficient plasma was fully corrected when HMW kininogen was added to the deficient plasma after depletion of kallikrein inhibitors. The functional and antigenic concentration of prekallikrein in plasma from four other HMW kininogen-deficient individuals was similarly corrected to normal after adding HMW kininogen. Addition of HMW kininogen increased the apparent prekallikrein activity in native normal plasma (as measured by esterase activity) but not in normal plasma in which inhibitors were inactivated. The apparent prekallikrein antigen concentration (as measured by radial immunodiffusion or electroimmunodiffusion) increased upon addition of HMW kininogen. Immunoelectrophoresis as well as gel filtration of normal plasma revealed the presence of free prekallikrein (17-38% of the total) in addition to the HMW kininogen-prekallikrein complex previously reported. This study emphasizes the influence of HMW kininogen on both functional and immunologic determinations of prekallikrein.