Human plasma prekallikrein (Fletcher factor) clotting activity and antigen in health and disease

Human plasma prekallikrein (Fletcher factor) clotting activity and antigen levels have been examined in various clinical conditions. Prekallikrein antigen was measured by a newly developed, specific, and sensitive radioimmunoassay. The assay had no demonstrable cross-reactivity with human urinary kallikrein nor, in the species tested, animal plasma prekallikrein. This assay was able to measure plasma kallikrein after its biological functions had been inactivated by plasma inhibitors. Normal human pooled plasma contained approximately 50 microgram/ml prekallikrein. Quantitative measurement of plasma prekallikrein was possible for concentrations as low as 0.3% of that of normal pooled plasma. A good correlation (correlation coefficient = 0.71) existed between titers of plasma prekallikrein measured by Fletcher factor clotting assays and radioimmunoassays among 40 normal subjects. Both prekallikrein clotting activity and antigen were significantly reduced in plasmas of patients with advanced hepatic cirrhosis or DIC. Prekallikrein activity and antigen were mildly decreased in plasmas or serums of patients with chronic renal failure and nephrotic syndrome but were normal in those of patients under treatment with warfarin or suffering from SLE, rheumatoid arthritis, sarcoidosis, or HANE. Human cord serum contained a lower titer of prekallikrein antigen than adult serum. Strenuous physical exercise did not significantly change plasma prekallikrein levels.     

A common neoepitope is created when the reactive center of C1-inhibitor is cleaved by plasma kallikrein, activated factor XII fragment, C1 esterase, or neutrophil elastase.

The reactive center of C1-inhibitor, a plasma protease inhibitor that belongs to the serpin superfamily, is located on a peptide loop which is highly susceptible to proteolytic cleavage. With plasma kallikrein, C1s and beta-Factor XIIa, this cleavage occurs at the reactive site residue P1 (Arg444); with neutrophil elastase, it takes place near P1, probably at residue P3 (Val442). After these cleavages, C1-inhibitor is inactivated and its conformation is modified. Moreover, in vivo, cleaved C1-inhibitor is removed from the blood stream more rapidly than the intact serpin, which suggests that proteolysis unmasks sites responsible for cellular recognition and the uptake of the cleaved inhibitor. In the study reported here, we show, using an MAb, that an identical neoepitope is created on C1-inhibitor after the cleavage of its exposed loop by plasma kallikrein, C1s, beta-Factor XIIa, and by neutrophil elastase.     

Evaluation of a microassay for human plasma prekallikrein

Current methods for determining plasma prekallikrein, one of three zymogens of the contact phase of plasma proteolysis, are laborious and impractical for general use in a clinical laboratory. Therefore, we have developed a simple, reliable assay using commercially available reagents. By use of the substrate H-D-Pro-Phe-Arg-p-nitroanilide-HCI (S-2302), a functional assay, performed in a 96-well microplate, was designed to measure prekallikrein in plasma. Measures were taken to destroy the naturally occurring plasma protease inhibitors of kallikrein without affecting the integrity of the plasma prekallikrein, which allowed complete activation of the zymogen to virtually 100% of predicted activity when compared with that of purified kallikrein. Besides permitting full activation, the use of low pH to destroy critical plasma protease inhibitors allowed the conversion of prekallikrein to kallikrein in as many as 44 plasma samples at one time without the tedious individual timing step usually required to activate each sample. An excellent correlation was found (r = 0.92) when this functional microassay was compared with a functional spectrophotometric assay performed in three subject populations: normal individuals, women receiving oral contraceptives (who frequently exhibit high plasma prekallikrein concentrations), and patients with liver disease (who manifest low plasma prekallikrein levels). This plasma prekallikrein microassay should facilitate the increased determination of plasma prekallikrein in pathophysiologic conditions as well as the monitoring of the progression of various diseases in which contact activation occurs.     

Characterization of three abnormal factor IX variants (Bm Lake Elsinore, Long Beach, and Los Angeles) of hemophilia-B. Evidence for defects affecting the latent catalytic site.

Abnormal factor IX variant proteins were isolated from the plasmas of three unrelated severe hemophilia-B families that had been previously shown to contain functionally impaired molecules immunologically similar to normal factor IX. The families studied were: (1) a patient with markedly prolonged ox brain prothrombin time, designated factor IX Bm Lake Elsinore (IXBmLE); (b) three patients (brothers) with moderately prolonged ox brain prothrombin time, designated factor IX Long Beach (IXLB); and (c) a patient with normal ox brain prothrombin time designated factor IX Los Angeles (IXLA). Each variant molecule comigrates with normal factor IX (IXN) both in the sodium dodecyl sulfate and in the nondenaturing alkaline gel electrophoresis. All three variant proteins are indistinguishable from IXN in their amino acid compositions, isoelectric points, carbohydrate distributions and number of gamma-carboxyglutamic acid residues. Each variant protein undergoes a similar pattern of cleavage by factor XIa/Ca2+ and by factor VIIa/Ca2+/tissue factor, and is activated at a rate similar to that observed for IXN. All of the three variant proteins also react with an anti-IXN monoclonal antibody that interferes with the binding of activated IXN(IXaN) to thrombin-treated factor VIIIC. However, in contrast to IXaN, the cleaved IXBmLE has negligible activity (approximately 0.2%), and cleaved forms of IXLA and IXLB have significantly reduced activity (approximately 5-6%) in binding to antithrombin-III/heparin, and in activating factor VII (plus Ca2+ and phospholipid) or factor X (plus Ca2+ and phospholipid) +/- factor VIII. These data, taken together, strongly indicate that the defect in these three variant proteins resides near or within the latent catalytic site. This results in virtually a complete loss of catalytic activity of the cleaved IXBmLE molecule and approximately 95% loss of catalytic activity of the cleaved IXLA and IXLB molecules.     

Fitzgerald Trait: Deficiency of a Hitherto Unrecognized Agent, Fitzgerald Factor, Participating in Surface-Mediated Reactions of Clotting, Fibrinolysis, Generation of Kinins, and the Property of Diluted Plasma Enhancing Vascular Permeability (PF/Dil)

The prolonged partial thromboplastin time observed in the plasma of a 71-yr-old asymptomatic man was related to the deficiency of a hitherto unrecognized agent. The patient's plasma also exhibited impaired surface-mediated fibrinolysis and esterolytic activity and impaired generation of kinins and of the property enhancing vascular permeability designated PF/Dil. The patient's plasma contained normal amounts of all known clotting factors except Fletcher factor (a plasma prekallikrein) which was present at a concentration of 10-15% of pooled normal plasma. Fletcher trait plasma, however, contained normal amounts of the agent missing from the patient's plasma and corrected the defects in clotting, fibrinolysis, and vascular permeability. Fletcher trait plasma was less effective in correcting generation of kinins and esterolytic activity, presumably because of the patient's partial deficiency of prekallikrein. The site of action of the factor deficient in the patient's plasma appeared to be subsequent to the activation of Hageman factor and plasma prekallikrein. A fraction of normal plasma, devoid of other clotting factors, corrected the defect in clotting in the patient's plasma; a similar fraction of the patient's plasma did not correct this abnormality. No evidence yet exists pointing to the familial nature of the patient's defect. Tentatively, the patient's disorder may be referred to by his surname as Fitzgerald trait, and the agent apparently deficient in his plasma as Fitzgerald factor.     

Protection by recombinant alpha 1-antitrypsin Ala357 Arg358 against arterial hypotension induced by factor XII fragment.

The specificity of serpin superfamily protease inhibitors such as alpha 1-antitrypsin or C1 inhibitor is determined by the amino acid residues of the inhibitor reactive center. To obtain an inhibitor that would be specific for the plasma kallikrein-kinin system enzymes, we have constructed an antitrypsin mutant having Arg at the reactive center P1 residue (position 358) and Ala at residue P2 (position 357). These modifications were made because C1 inhibitor, the major natural inhibitor of kallikrein and Factor XIIa, contains Arg at P1 and Ala at P2. In vitro, the novel inhibitor, alpha 1-antitrypsin Ala357 Arg358, was more efficient than C1 inhibitor for inhibiting kallikrein. Furthermore, Wistar rats pretreated with alpha 1-antitrypsin Ala357 Arg358 were partially protected from the circulatory collapse caused by the administration of beta-Factor XIIa.     

Determination of prekallikrein in human plasma: optimal conditions for activating prekallikrein

A method for the assay of human plasma prekallikrein in which a chromogenic synthetic tripeptide, PPAN, is used as a substrate for kallikrein is described. The conversion of prekallikrein to kallikrein is achieved by cold activation (0 degrees C) with water-soluble dextran sulfate. Conditions for obtaining optimal amounts of free kallikrein with respect to concentration of dextran sulfate, activation time, inhibitors (C-1-inactivator), and requirement of factor XII have been determined. The activation procedure is compared to other known procedures. The assay system was worked out for pooled normal plasma and is applicable to any plasma sample not liable to unwanted preactivation or incomplete inactivation, as revealed by control experiments. A survey in 15 apparently health individuals showed a mean activity of 476 +/- 58 (S.D.) mU/ml with a range of 385 to 586 mU/ml.     

THE FIRST COMPONENT OF THE KININ-FORMING SYSTEM IN HUMAN AND RABBIT PLASMA : ITS RELATIONSHIP TO CLOTTING FACTOR XII (HAGEMAN FACTOR)

The isolation and characterization of the first component of the kinin-forming system in human and rabbit plasma are presented. Functionally, the molecule is the precursor of the activator of prekallikrein (Pre-PKA) and evidence is presented that it is identical with Hageman factor (clotting factor XII). The component from each plasma possessed similar characteristics. This molecule was found to have a mol wt of 110,000 and sedimentation rate of 4.6S. It migrated in electrophoresis as a β-globulin, having an isoelectric point of 6.1. Upon activation with glass, kaolin, diatomaceous earth, ellagic acid, or trypsin, the activated molecule converted purified prekallikrein (prokininogenase) to the active enzyme. Clot-promoting activity was associated with the capacity to activate prekallikrein through each procedure of isolation. The clot-promoting factor was in precursor form, requiring treatment with kaolin or trypsin to gain activity. Evidence indicated that the protein was Hageman factor (factor XII): it promoted clotting of factor XII-deficient, but not Factor XI- or IX-deficient plasma, and did not convert fibrinogen to fibrin it bound to and was activated by kaolin or other negatively charged particles in the presence of chelating agents; the activation by kaolin could be prevented by pretreating the kaolin with hexadimethrine bromide (H Br); prekallikrein-activating and clot-promoting activities were identical in their physical properties; and the prekallikrein activator could not be detected in Hageman factor-deficient plasma. Activation of Hageman factor was accompanied by cleavage of the molecule into several fragments, one of which possessed prekallikrein-activating (PKA) and clot-promoting properties. The PKA fragment sedimented at 2.6S and by gel filtration was found to have a molecular weight of 32,000. The PKA possessed only 1/50 the clot-promoting capacity of the freshly activated native molecule.     

Plasma prekallikrein assay: reversible inhibition of C-1 inhibitor by chloroform and its use in measuring prekallikrein in different mammalian species

The assay of plasma prekallikrein requires activation of prekallikrein to kallikrein and sufficient inactivation of the plasma protease inhibitors of kallikrein to accurately measure the generated kallikrein activity. One method of elimination of the plasma protease inhibitors to kallikrein is to chemically pretreat the plasma. Methylamine has previously been employed to selectively inactivate alpha 2-macroglobulin. Our study examines the effect of sequential preincubation of plasma with chloroform and methylamine on the plasma prekallikrein assay. Chloroform was demonstrated to be a chemical inhibitor of purified C-1 inhibitor, but alpha 2-macroglobulin was not. Chloroform inhibition of C-1 inhibitor was not caused by precipitation of the protein into the interface between the water and organic solvent phase. Greater than 95% of C-1 inhibitor antigen was recovered in the supernatant of chloroform-treated purified C-1 inhibitor, and chloroform-saturated buffer inhibited purified C-1 inhibitor. Chloroform did not dissociate a preformed complex of kallikrein and C-1 inhibitor, but its inhibition of C-1 inhibitor was reversible. The addition of methylamine to plasma pretreated with chloroform in the plasma prekallikrein assay allowed for only a slight increase in the amount of kallikrein measured at 1 minute kaolin activation times, but provided for sustained measurement of activated prekallikrein when kaolin activation times were 5 to 7 minutes. Without chemical pretreatment, prekallikrein was not measurable in rabbit plasma. Both rabbit and pig plasma prekallikrein was measurable after exposure of the plasma to chloroform and methylamine, although the peak activation times and the contribution of each animals' protease inhibitors varied with the species. Our results show that chloroform is a reversible inhibitor of C-1 inhibitor, and that the plasma prekallikrein assay in which it is used is useful for the measurement of prekallikrein in nonhuman mammalian plasma samples.     

Characterization of the defect in activation of factor IX Chapel Hill by human factor XIa.

Factor IXChapel Hill (Factor IXCH), an abnormal Factor IX molecule isolated from the plasma of a patient with mild hemophilia B, has previously been shown to exhibit delayed activation by Factor XIa and calcium. In this study, we have found that Factor IXCH is cleaved upon incubation with human Factor XIa and calcium; however, cleavage of this protein is not observed by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis under nonreducing conditions. Under reducing conditions, the rate of disappearance of the zymogen parallels both the appearance of the heavy chain and the generation of clotting activity. In addition, a protein band that migrates with an apparent molecular weight of 45,000 also increases in parallel with clotting activity. Factor IXCH and normal Factor IX (Factor IXN), after incubation with Factor XIa and calcium, were subjected to amino terminal sequence analysis. Activated Factor IXN is cleaved at an arginine-alanine (Arg-Ala) bond and an arginine-valine (Arg-Val) bond as demonstrated by formation of the three amino terminal sequences corresponding to the amino terminal of the light chain, heavy chain, and activation peptide. However, activated Factor IXCH has only two amino terminal sequences, corresponding to the original amino terminal sequence and the heavy chain (formed by cleavage at the Arg-Val bond). It is concluded that the major defect in Factor IXCH is the inability of Factor XIa to cleave the Arg-Ala bond at a significant rate. The rate of formation of clotting activity of Factor IXCH is approximately 60% of the rate of formation of clotting activity of Factor IXN. The specific clotting activity of activated Factor IXCH is between 20 and 33% of activated Factor IXN.     

Activation of Human Factor VII in Plasma and in Purified Systems: ROLES OF ACTIVATED FACTOR IX, KALLIKREIN, AND ACTIVATED FACTOR XII

Factor VII can be activated, to a molecule giving shorter clotting times with tissue factor, by incubating plasma with kaolin or by clotting plasma. The mechanisms of activation differ. With kaolin, activated Factor XII (XII(a)) was the apparent principal activator. Thus, Factor VII was not activated in Factor XII-deficient plasma, was partially activated in prekallikrein and high-molecular weight kininogen (HMW kininogen)-deficient plasmas, but was activated in other deficient plasmas. After clotting, activated Factor IX (IX(a)) was the apparent principal activator. Thus, Factor VII was not activated in Factor XII-,HMW kininogen-, XI-, and IX-deficient plasmas, but was activated in Factor VIII-, X-, and V-deficient plasmas. In further studies, purified small-fragment Factor XII(a) (beta-XII(a)), kallikrein, and Factor IX(a) were added to partially purified Factor VII and to plasma. High concentrations of beta-XII(a) activated Factor VII in a purified system; much lower concentrations of beta-XII(a) activated Factor VII in normal plasma but not in prekallikrein or HWM kininogen-deficient plasmas. Kallikrein alone failed to activate partially purified Factor VII but did so when purified Factor IX was added. Kallikrein also activated Factor VII in normal, Factor XII-, and Factor IX-deficient plasmas. Purified Factor IX(a) activated partially purified Factor VII and had no additional indirect activating effect in the presence of plasma. These results demonstrate that both Factor XII(a) and Factor IX(a) directly activate human Factor VII, whereas kallikrein, through generation of Factor XII(a) and Factor IX(a), functions as an indirect activator of Factor VII.     

Plasma Kallikrein Activation and Inhibition during Typhoid Fever

As an ancillary part of a typhoid fever vaccine study, 10 healthy adult male volunteers (nonimmunized controls) were serially bled 6 days before to 30 days after ingesting 10(5)Salmonella typhi organisms. Five persons developed typhoid fever 6-10 days after challenge, while five remained well. During the febrile illness, significant changes (P < 0.05) in the following hematological parameters were measured: a rise in alpha(1)-antitrypsin antigen concentration and high molecular weight kininogen clotting activity; a progressive decrease of platelet count (to 60% of the predisease state), functional prekallikrein (55%) and kallikrein inhibitor (47%) with a nadir reached on day 5 of the fever and a subsequent overshoot during convalescence. Despite the drop in functional prekallikrein and kallikrein inhibitor, there was no change in factor XII clotting activity or antigenic concentrations of prekallikrein and the kallikrein inhibitors, C1 esterase inhibitor (C1-INH) and alpha(2)-macroglobulin. Plasma from febrile patients subjected to immunoelectrophoresis and crossed immunoelectrophoresis contained a new complex displaying antigenic characteristics of both prekallikrein and C1-INH; the alpha(2)-macroglobulin, antithrombin III, and alpha(1)-antitrypsin immunoprecipitates were unchanged. Plasma drawn from infected-well subjects showed no significant change in these components of the kinin generating system. The finding of a reduction in functional prekallikrein and kallikrein inhibitor (C1-INH) and the formation of a kallikrein C1-INH complex is consistent with prekallikrein activation in typhoid fever. The correlation of these changes with the drop in platelet count suggests that a common mechanism may be responsible.     

The role of prekallikrein and high-molecular-weight kininogen in the contact activation of Hageman factor (factor XII) by sulfatides and other agents

Hageman factor (HF, factor XII), adsorbed to negatively charged agents, is transformed to an activated state in which it initiates reactions of the intrinsic pathway of thrombin formation by activating plasma thromboplastin antecedent (PTA, factor XI). High-molecular-weight kininogen (HMWK, Fitzgerald factor) and plasma prekallikrein accelerate these early steps in the clotting process. Questions have been raised about the role of HMWK in the activation of Hageman factor by surfaces. In the present studies, we report that the activation of purified human HF by sulfatides, ellagic acid, kaolin, or glass occurred in the absence of HMWK. Indeed, small amounts of HMWK inhibited activation of HF by ellagic acid. Physiological concentration of HMWK had little or no influence on the activation of HF by sulfatides, kaolin, or glass, but higher concentrations (3 to 6 times more) showed the same inhibitory effect as after activation by ellagic acid. This inhibitory property of HMWK may be attributed to competitive binding of HF and HMWK on the surface of the activating agents. In fact, when HF was added to kaolin or glass that had been incubated with HMWK and then washed, the inhibitory effect persisted, indicating HMWK that was bound to the surface blocked activation of HF. Studies with 125I-HF and 125I-HMWK supported this interpretation. Plasma prekallikrein accelerated activation of the amidolytic properties of HF by sulfatides, kaolin, or glass but did not influence activation of HF by ellagic acid. In the presence of plasma kallikrein, HMWK at moderate concentrations slightly accelerated the rate of activation of HF by activating agents other than ellagic acid. Higher concentrations of HMWK counteracted both the accelerating effect of prekallikrein and the inhibitory effect observed when HF was incubated with an excess of kaolin. These experiments, then, support the view that the procoagulant function of HMWK is localized to a point subsequent to the activation of HF.     

Recombinant C1 inhibitor P5/P3 variants display resistance to catalytic inactivation by stimulated neutrophils.

Proteolytic inactivation of serine protease inhibitors (serpins) by neutrophil elastase (HNE) is presumed to contribute to the deregulation of plasma cascade systems in septic shock. Here, we report a supplementary approach to construct serpins, in our case C1 inhibitor, that are resistant to catalytic inactivation by HNE. Instead of shifting the specificity of alpha 1-antitrypsin towards the proteases of the contact activation and complement systems, we attempted to obtain a C1 inhibitor species which resists proteolytic inactivation by HNE. 12 recombinant C1 inhibitor variants were produced with mainly conservative substitutions at the cleavage sites for HNE, 440-Ile and/or 442-Val. Three variants significantly resisted proteolytic inactivation, both by purified HNE, as well as by activated neutrophils. The increase in functional half-life in the presence of FMLP-stimulated cells was found to be 18-fold for the 440-Leu/442-Ala variant. Inhibitory function of these variants was relatively unimpaired, as examined by the formation of stable complexes with C1s, beta-Factor XIIa, kallikrein, and plasmin, and as determined by kinetic analysis. The calculated association rate constants (k(on)) were reduced twofold at most for C1s, and appeared unaffected for beta-Factor XIIa. The effect on the k(on) with kallikrein was more pronounced, ranging from a significant ninefold reduction to an unmodified rate. The results show that the reactive centre loop of C1 inhibitor can be modified towards decreased sensitivity for nontarget proteases without loss of specificity for target proteases. We conclude that this approach extends the possibilities of applying recombinant serpin variants for therapeutic use in inflammatory diseases.     

Plasma prekallikrein: quantitative determination by direct activation with Hageman factor fragment (beta-XIIa)

This report describes a plasma prekallikrein assay which, unlike methods that employ contact activation, is not affected by the factor XII or HMW kininogen content of the plasma analyzed. In this assay beta-XIIa, a potent fluid-phase activator of prekallikrein, is added to diluted plasma in the presence of 20% acetone (to inactivate kallikrein inhibitors) at 30 degrees C and the kallikrein generated is measured with the chromogenic substrate S-2302. Prekallikrein is fully activated under these conditions and the activity remains stable for at least 30 hr. The mean prekallikrein concentration in plasma samples from 24 healthy individuals was 1.50 +/- 0.35 (S.D.) S-2302 U/ml, corresponding to 20.3 +/- 4.7 micrograms/ml prekallikrein (the specific activity of highly purified human prekallikrein was determined to be 74 S-2302 U/mg). In contrast, the mean concentration in five plasma samples from patients deficient in HMW kininogen was 0.38 +/- 0.02 S-2302 U/ml. No activity was generated in prekallikrein-deficient plasma, and essentially normal levels (1.35 +/- 0.18 S-2302 U/ml) were measured in plasmas from three patients with factor XII deficiency. Plasma prekallikrein was also quantitated by radial immunodiffusion, which gave results similar to those obtained by functional assay with beta-XIIa. The determination of plasma prekallikrein by direct activation with beta-XIIa in the presence of acetone offers several advantages over the use of contact activators such as dextran sulfate. These advantages include complete inactivation of kallikrein inhibitors and total activation of prekallikrein (even in plasmas deficient in other contact factors) without simultaneous generation of plasmin.     

Abnormal hemostasis in a knock-in mouse carrying a variant of factor IX with impaired binding to collagen type IV

Summary.  Background : Factor IX binds to collagen type IV, but this binding has no known consequence. Objectives : To determine the effect of reduced binding of FIX to collagen IV. Methods : We constructed and characterized 'knock-in' mice containing the mutation lysine 5 to alanine (K5A) in the Gla domain of their FIX. The K5A mutation dramatically reduced the affinity of FIX for collagen type IV, but had no measurable effect on platelet binding, phospholipid binding, or in vitro clotting activity. However, K5AFIX mice had a mild bleeding tendency, despite their in vitro clotting activity being normal. Hemostatic protection from delayed rebleeding was intermediate between wild-type and hemophilia B mice (which had no detectable clotting activity); moreover, survival of K5A FIX mice after nascent clot removal was dramatically improved as compared with hemophilia B mice. Importantly, there was no detectable difference between K5AFIX and wild-type mice in either a laser-induced thrombosis model or the chromogenic FIX activity assay. In contrast, after ferric chloride injury, which exposes collagen IV as well as other basement membrane proteins, intravital microscopy revealed that vessel occlusion was significantly slower in K5AFIX mice than in wild-type mice. Conclusions : Our results indicate that the FIX molecule with decreased affinity for collagen IV has altered hemostatic properties in vivo and that the binding of FIX to collagen IV probably plays a significant functional role in hemostasis.     

Mechanized assay of plasma prekallikrein by activation with Pseudomonas aeruginosa elastase and amidolysis of chromogenic substrate.

An automated assay of plasma prekallikrein is described. Prekallikrein was converted to kallikrein with Pseudomonas aeruginosa elastase, and the hydrolytic activity of kallikrein to H-D-Pro-Phe-Arg-paranitroanilide subsequently measured.

The conversion was complete within 8 minutes and the amidolytic activity remained stable at least another 10 min at 37 ° C. This method worked in plasma deficient in Hageman factor (blood coagulation factor XII). Using anti-prekallikrein antibody and plasma deficient in prekallikrein, the amidolytic activity generated in normal plasma was identified as due to kallikrein. With plasma samples, the coefficients of variation (CV) for multiple measurements within run (n = 10) and between run (n = 10) were as low as 5.0% and 6.6%, respectively, and the minimum measurable concentration of prekallikrein in plasma was 10% of the normal level.     

Mechanized assay of plasma prekallikrein by activation with Pseudomonas aeruginosa elastase and amidolysis of chromogenic substrate

An automated assay of plasma prekallikrein is described. Prekallikrein was converted to kallikrein with Pseudomonas aeruginosa elastase, and the hydrolytic activity of kallikrein to H-D-Pro-Phe-Arg-paranitroanilide subsequently measured.The conversion was complete within 8 minutes and the amidolytic activity remained stable at least another 10 min at 37 ° C. This method worked in plasma deficient in Hageman factor (blood coagulation factor XII). Using anti-prekallikrein antibody and plasma deficient in prekallikrein, the amidolytic activity generated in normal plasma was identified as due to kallikrein. With plasma samples, the coefficients of variation (CV) for multiple measurements within run (n = 10) and between run (n = 10) were as low as 5.0% and 6.6%, respectively, and the minimum measurable concentration of prekallikrein in plasma was 10% of the normal level.     

The Binding and Cleavage Characteristics of Human Hageman Factor during Contact Activation: A COMPARISON OF NORMAL PLASMA WITH PLASMAS DEFICIENT IN FACTOR XI, PREKALLIKREIN, OR HIGH MOLECULAR WEIGHT KININOGEN

The ability of human Hageman factor (coagulation factor XII) to bind to a glass surface and its susceptibility to limited proteolytic cleavage during the contact activation of plasma have been studied using normal human plasma and plasmas genetically deficient in factor XI, prekallikrein, or high molecular weight kininogen (HMWK). When diluted normal plasma containing ¹²⁵I-Hageman factor was exposed to a glass surface for varying times, the Hageman factor was found to bind to the surface, and within 5 min became maximally cleaved from its native 80,000 mol wt to yield fragments of 52,000 and 28,000 mol wt. Hageman factor in factor XI-deficient plasma behaved similarly. In prekallikrein-deficient plasma, the binding of Hageman factor to the glass surface occurred at the same rate as in normal plasma but the cleavage was significantly slower, and did not reach maximum until 60 min of incubation. Cleavage of Hageman factor in HMWK-deficient plasma occurred at an even slower rate, with greater than 110 min of incubation required for maximal cleavage, although the rate of binding to the glass was again the same as in normal plasma. Normal rates of cleavage of Hageman factor were observed for the deficient plasmas after reconstitution with purified human prekallikrein or HMWK, respectively. These observations suggest that normal contact activation in plasma is associated with proteolytic activation of surfacebound Hageman factor.     

Anaphylactic release of a prekallikrein activator from human lung in vitro.

We have demonstrated the in vitro IgE-mediated release of a prekallikrein activator from human lung. The lung prekallikrein activator was partially purified by sequential chromatography on sulfopropyl-Sephadex, DEAE-Sephacel, and Sepharose 6B. Purified human prekallikrein was converted to its active form (kallikrein) by the lung protease. The generated kallikrein was shown to be biologically active; that is, it generates bradykinin from purified human high-molecular weight kininogen and also cleaves benzoyl-propyl-phenyl-arginyl-p-nitroanilide, a known synthetic substrate of kallikrein. The lung prekallikrein activator differs from the known physiologic activators of prekallikrein (the activated forms of Hageman factor) with respect to: (a) size (it has a mol wt of approximately 175,000); (b) synthetic substrate specificity (D-propyl/phenyl/arginyl-p-nitroanilide is a substrate for the activated forms of Hageman factor, but not the lung protease); (c) antigenic specificity (an anti-Hageman factor immunoadsorbent column did not remove significant amounts of the lung protease, while it removed most of the activity of activated Hageman factor fragments); and (d) inhibition profile (the lung proteases was not inhibited by corn trypsin inhibitor). This prekallikrein activator provides a physiologic mechanism by which prekallikrein can be directly activated during IgE-mediated reactions of the lung. While the role of this lung prekallikrein activator in immediate hypersensitivity reactions and in other inflammatory processes is not clear, it does represent a first and important interface between IgE-mediated reactions and the Hageman factor-dependent pathways of the inflammatory response.