Kinetic analysis of the interaction of human tissue kallikrein with single-chain human high and low molecular weight kininogens.

Human low molecular weight kininogen (LMWK) and high molecular weight kininogen (HMWK) have been purified to apparent homogeneity as intact, single-chain molecules. When they interacted with homologous urinary kallikrein, 0.9 mol of kinin per mol of substrate was released from LMWK and 0.7 mol of kinin per mol of substrate was released from HMWK. These functionally and structurally intact substrates have been used to obtain the kinetic constants for kinin release by purified human tissue kallikreins. With human urinary kallikrein, apparent second-order rate constants (kcat/Km) of 1.46 X 105, 8.6 X 104, and 5.08 X 104 M-1.S-1 were obtained with LMWK, HMWK, and alpha-N-p-tosyl-L-arginine methyl ester (TAMe), respectively; with human pancreatic kallikrein, values of 8.7 X 103 and 7.3 X 104 M-1.S-1 were obtained with HMWK and TAMe. These values, which are comparable to those obtained for other enzyme-protein substrate interactions, indicate that LMWK is only slightly preferred to interactions, indicate that LMWK is only slightly preferred to HMWK as the natural substrate for urinary kallikrein and that HMWK as the natural substrate for urinary kallikrein and that HMWK is a somewhat better substrate for urinary kallikrein than for pancreatic kallikrein. Although the data obtained have been shown by NaDodSO4/polyacrylamide gel electrophoresis to reflect cleavage of the substrate at two points, the linear Line-weaver-Burk plots suggest that one cleavage is rate limiting. Because the plasma concentrations of both LMWK and HMWK are approximately 1/10th the Km values obtained, substrate concentration may also play a role in determining the rate at which tissue kallikreins release kinins from kininogen substrates either in the circulation or extravascularly.     

Detection of in vitro and in vivo cleavage of high molecular weight kininogen in human plasma by immunoblotting with monoclonal antibodies

Purified human high-mol-wt kininogen (HMWK), the cofactor of the contact phase of blood coagulation, migrated as a single band (approximately 110,000 mol wt) in a continuous buffer sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), but appeared as two separated bands (approximately 120,000 and 105,000 mol wt) when analyzed in a discontinuous buffer SDS-PAGE system. After elution from SDS polyacrylamide gels, each of the two bands showed coagulant activity. Six murine monoclonal antibodies (Mabs) against HMWK were produced and purified. In immunoblotting studies, three Mabs bound to the isolated alkylated heavy chain and one to the alkylated light chain of HMWK, whereas the remaining two bound only to the single-chain or unreduced two-chain molecule. None of the Mabs inhibited the clotting activity of HMWK or its binding to kaolin. Two of the Mabs, one directed against the light chain and one against the heavy chain, were used as specific probes to study HMWK in plasma samples using an immunoblotting technique. The anti-light chain Mab identified two distinct bands (approximately 120,000 and approximately 105,000 mol wt) in normal human plasma, but not in plasma from patients with hereditary HMWK deficiency. The anti-heavy chain Mab detected two additional bands (approximately 60,000 and approximately 54,000 mol wt) corresponding to low-mol-wt kininogen (LMWK) in normal plasma. A sensitive and specific quantitative immunoblotting assay of HMWK antigen in plasma was developed. Moreover, the immunoblotting technique with the anti-light chain Mab was used to detect the cleavage of HMWK in plasma samples after in vitro or in vivo activation of the contact system. The anti- light chain Mab demonstrated in vivo activation and cleavage of HMWK during an angioedema attack in a patient with hereditary angioedema and C1-inhibitor deficiency.     

Effect of cleavage of the heavy chain of human plasma kallikrein on its functional properties

Human plasma kallikrein consists of an N-terminal heavy chain of molecular weight (mol wt) 52,000, linked by disulfide bonds to two light chain variants (mol wt 36,000 or 33,000). Although the active catalytic site of kallikrein resides on the C-terminal light chain, the role of the N-terminal heavy chain is less clear. We therefore studied an enzyme designated beta-kallikrein, containing a single cleavage in the heavy chain (mol wt 28,000 + 18,000) and compared it to the enzyme, alpha-kallikrein, with an intact heavy chain. The rates of inactivation by C1 inhibitor of plasma alpha- and beta-kallikreins were kinetically identical, as measured by residual amidolytic activity, after various times of incubation with the inhibitor. Both enzymes reacted completely with C1 inhibitor after 18 hours and formed identical C1 inhibitor- kallikrein complexes of mol wt 195,000. The rate of activation of factor XII by alpha-kallikrein and beta-kallikrein was similar. In contrast, the rate of cleavage of high molecular weight kininogen (HMWK) by alpha-kallikrein was at least fivefold faster and the ratio of coagulant activity to amidolytic activity was fourfold greater than for beta-kallikrein. Plasma alpha-kallikrein, at concentrations potentially achievable in plasma, induced aggregation of neutrophils, but beta-kallikrein failed to elicit this response. In addition, human neutrophils pretreated with cytochalasin B released 2.46 +/- 0.10 microgram/10(7) cells of elastase antigen, but beta-kallikrein released only 0.25 +/- 0.10 micrograms/10(7) cells. These observations suggest that cleavage of the heavy chain influences the rate of cleavage of HMWK and decreases its coagulant activity. Moreover, an intact heavy chain appears to be requisite to support the ability of kallikrein to aggregate neutrophils and release elastase.     

Radioimmunoassays of human high and low molecular weight kininogens in plasmas and platelets

Radioimmunoassays of human high molecular weight kininogen (HMWK) and low molecular weight kininogen (LMWK) were developed using antibodies directed against the light and the heavy chains of kallikrein-cleaved HMWK. With the anti-light chain antibodies, the radioimmunoassay was specific for HMWK with a detection limit of 0.4 ng. The anti-heavy chain antibodies were used to quantify the concentration of total kininogen antigens. In four different plasmas with a congenital deficiency in HMWK procoagulant activity, there was no detectable antigen in two cases and trace amounts, less than 1 micrograms/ml in the other plasmas (normal concentration: 72 +/- 6 micrograms/ml). In the absence of HMWK, the radioimmunoassay performed with the anti-heavy chain antibodies was specific for LMWK. The amount of LMWK was different in each of these patients' plasmas, ranging from no detectable antigen, i.e. less than 0.15 micrograms/ml, to a normal content. Antigens immunologically indistinguishable from plasma kininogens were detected in lysates of five times washed platelets. HMWK antigen concentration was 3.17 +/- 0.87 micrograms per 10(11) platelets (mean value in 11 donors). LMWK was also present in platelet lysates and the relative concentration versus HMWK was the same as in plasma.     

High molecular weight kininogen: localization in the unstimulated and activated platelet and activation by a platelet calpain(s)

High mol wt kininogen (HMWK), the major cofactor-substrate of the contact phase of coagulation, is contained within and secreted by platelets. Studies have been performed to localize platelet HMWK in both the unstimulated and activated platelet and to ascertain the effect of platelet enzymes on HMWK itself. On platelet subcellular fractionation, platelet HMWK was localized to alpha-granules, and platelets from a patient with a deficiency of these granules (gray platelet syndrome) had 28% normal platelet HMWK. Platelet HMWK, in addition to being secreted from the platelet, was also localized to the surface of the platelet when activated. Using a competitive enzyme- linked immunosorbent assay for HMWK as an indirect antibody consumption assay, the external membrane of thrombin-activated platelets as well as the releasate from these stimulated platelets had 17 ng HMWK antigen/10(8) platelets available, whereas unstimulated platelets and their supernatant had only 4.9 and 4.2 ng HMWK/10(8) platelets present, respectively. The anti-HMWK antibody consumption by activated normal platelets was specific for membrane-expressed platelet HMWK, since activated platelets from a patient with total kininogen deficiency did not adsorb the anti-HMWK antibody. Enzymes in the cytosolic fraction of platelets cleaved 125I-HMWK (mol wt 120,000) into a mol wt 100,000 polypeptide as well as smaller products at mol wt 74,000, mol wt 62,000, mol wt 47,000, and a few components below mol wt 45,000. No cleavage products were observed when DFP and leupeptin were present. The cleavage of HMWK was specifically prevented by inhibitors of calcium-activated cysteine proteases (leupeptin, N-ethylmaleimide, iodoacetamide, and EDTA) but not by inhibitors of serine proteases (DFP, benzamidine, soybean trypsin inhibitor, or aprotinin). Platelet cytosol increased the coagulant activity of exogenous purified HMWK with maximum HMWK coagulant activity (35-fold) occurring within ten minutes of exposure to platelet cytosol. Treatment of platelet cytosol with leupeptin prevented the increase in the coagulant activity of exogenous HMWK. These studies indicate that activated platelets express platelet HMWK on their external membrane and platelet enzymes can cleave and increase the coagulant activity of exogenous HMWK.     

Cleavage of human high-molecular weight kininogen by purified kallikreins and upon contact activation of plasma

To study the digestion pattern of human high-molecular weight (mol wt) kininogen (HMWK) in plasma during contact activation we have prepared monoclonal antibodies (MoAbs) to the light-chain (LC) and the heavy-chain moiety of HMWK. One MoAb from each set was purified, and neither MoAb inhibited the clotting activity of HMWK. In enzyme-linked immunosorbent assay and immunoblotting experiments neither antibody bound to kininogen-deficient plasma. Digestion of purified HMWK with plasma kallikrein yielded, on reduced sodium dodecyl sulfate gels, two LC forms, at 62 and 49 kd, respectively. Digestion of HMWK with tissue kallikrein (TK) yielded mainly the 62-kd form. In immunoblot analyses of these digests, the anti-LC MoAb detected products at 62 and 49 kd respectively. With plasma kallikrein, the 62-kd species slowly shifted to 49 kd, and with TK, the 62-kd species accumulated with time. Anti-LC MoAb was also used as a probe in immunoblotting experiments to study the digestion pattern of HMWK in whole plasma activated with kaolin or dextran sulfate. In activated normal pooled plasma (NHP) and factor XI-deficient plasma, native HMWK (mol wt, 115 kd) was cleaved within five to ten minutes, and two LC forms at 62 and 49 kd were detected. In kaolin-activated prekallikrein (PK)-deficient plasma, the disappearance of the 115-kd form was relatively slow, and only the 62-kd form of LC was seen. HMWK was not cleaved when factor XII-deficient plasma was incubated with kaolin. LC-dependent coagulant activity paralleled the presence of LC bands seen in the immunoblots, and lower-mol wt fragments of LC were not identified. These data indicate that in activated NHP two forms of LC of HMWK (62 and 49 kd) are formed sequentially. Further, the LC-dependent coagulant activity remains detectable long enough to suggest that proteolytic inactivation of LC is too slow to be an important control mechanism.     

Proteolytic inactivation of human factor VIII procoagulant protein by activated human protein C and its analogy with factor V

Purified human factor VIII procoagulant protein (VIII:C) was treated with purified human activated protein C (APC) and the loss of VIII:C activity correlated with proteolysis of the VIII:C polypeptides. APC proteolyzed all VIII:C polypeptides with mol wt = 92,000 or greater, but not the doublet at mol wt = 79-80,000. These results and our previous thrombin activation studies of purified VIII:C, are analogous with similar studies of factor V and form the basis for the following hypothesis: activated VIII:C consists of heavy and light chain polypeptides [mol wt = 92,000 and mol wt = 79-80,000 (or 71-72,000), respectively] which are similar in Mr to the heavy and light chains of activated factor V. Thrombin activates VIII:C and V by generating these polypeptide chains from larger precursors and APC inactivates both molecules by cleavage at a site located in the heavy chain region of activated VIII:C and V.     

Relationship of contact activation cofactor (CAC) procoagulant activity to kininogen.

Contact activation cofactor (CAC) facilitates the interaction of factors XI and XII. Patients lacking CAC have a coagulation defect and are deficient in high molecular weight kininogen. The coincidence of these two defects suggests that a single protein may be responsible for both physiologic functions. Immunologic and activity studies have been made on isolated CAC to clarify the relationship between CAC and kininogen. CAC forms a single precipitin line with anti-human kininogen, and antikininogen neutralizes CAC activity. CAC and high molecular weight kininogen show a reaction of identity on immunodiffusion against rabbit anti-CAC. Anti-CAC forms two precipitin lines with normal plasma which can be identified as high and low molecular weight kininogen. Monospecific immunoabsorbed anti-CAC forms a single precipitin line with plasma high molecular weight kininogen and neutralizes CAC activity. Cleavage of kinin fragment from CAC by insoluble trypsin or kalikrein does not proportionally reduce procoagulant activity. CAC neutralized by anti-CAC can release kinins on exposure to trypsin or kallikrein. The results support the conclusions that CAC procoagulant activity is a function of high molecular weight kininogen, that antigenic determinants unique to high molecular weight kininogen are shared by the CAC portion of the molecule, and that the clotting reactions may occur at a site removed from the kinin peptide.     

Kallikrein-like activity of crotalase, a snake venom enzyme that clots fibrinogen.

During the amino acid sequence determination of crotalase (EC 3.4.21.30), the thrombin-like enzyme from the venom of Crotalus adamanteus (eastern diamondback rattlesnake), we found that, in addition to the expected structural homology with bovine thrombin (EC 3.4.21.5), there was even greater homology with porcine pancreatic kallikrein (EC 3.4.21.8). In exploring further the similarities between crotalase and kallikrein, several striking observations were made. First, crotalase was rapidly and specifically inhibited by the tripeptide affinity labeling derivative prolylphenylalanylarginine chloromethyl ketone, which is known to be a specific inhibitor of kallikrein. Second, NaDodSO4/acrylamide gel electrophoresis revealed that crotalase cleaves the plasma kallikrein-susceptible bonds in human high molecular weight kininogen, producing an intermediate with procoagulant activity. Crotalase-catalyzed cleavage of high molecular weight kininogen also liberates kinin as evidenced by rat blood pressure bioassay. Finally, crotalase exhibits substrate specificity not only for the thrombin chromogenic substrate S-2238 but also for the kallikrein substrates S-2302 and S-2266. Interestingly, one of the other reactions catalyzed by plasma kallikrein, the activation of plasminogen, was not one of the activities exhibited by crotalase.     

A monoclonal anti-human plasma prekallikrein antibody that inhibits activation of prekallikrein by factor XIIa on a surface

Of five IgGI/k murine monoclonal anti-human prekallikrein antibodies produced (MAbs), MAb 13G11 was selected for studying interaction of prekallikrein with factor XII and high-mol-wt kininogen (HMWK) during activation on a surface. Immunoblots from sodium dodecyl sulfate (SDS) gels showed that this MAb recognizes two variants (88 kd and 85 kd) of prekallikrein and kallikrein both in purified proteins and normal plasma. Under reducing conditions, kallikrein exhibits the epitope on the heavy chain but not on the light chains. Preincubation of MAb 13G11 with prekallikrein (added to prekallikrein-deficient plasma) or with normal plasma inhibited surface activation of prekallikrein 60% to 80%, as judged by amidolytic and coagulant assays. In normal plasma, inhibition by the Fab fragments was 87% of that with the entire MAb. Inhibition was not by competition between the MAb and HMWK, since neither binding of 13G11 to prekallikrein (coated on microtiter plates) was inhibited by an excess of HMWK, nor was hydrolysis of HMWK by kallikrein inhibited by 13G11. Using purified proteins in a system mimicking contact activation, inhibition by 13G11 of prekallikrein activation by factor XIIa, HMWK, and kaolin present was approximately 80%. Decreased inhibition (55% to 25%) occurred without HMWK or when kallikrein was used instead of prekallikrein. Kallikrein activity was not inhibited by 13G11 Fab fragments. These results indicate that the effect of 13G11 in plasma was neither dissociation of prekallikrein- HMWK complex nor a direct effect on kallikrein activity. Similar to the results in plasma, activation of prekallikrein, HMWK present, by factor XIIa bound to kaolin, was inhibited approximately 70% by 13G11. The results suggest a previously unrecognized site on the prekallikrein (heavy chain) required for its interaction with factor XIIa, either shared with the 13G11 epitope or located in very close proximity. The inhibition of kallikrein by intact 13G11 indicates that its binding site on the heavy chain is sterically related to the active site (light chain).     

Inhibition of human bronchial kallikrein in asthma

Human bronchial kallikrein (HBK) is the major kinin-generating enzyme in the airways of asthmatic subjects. We examined the in vitro inhibition of HBK and its in vivo regulation in asthma. HBK kininogenase activity was measured by cleavage of radiolabeled purified high molecular weight kininogen (HMWK) (125I HMWK). Functional inhibition of the enzyme was present after co-incubation with either normal human plasma (NHP) or preparations of alpha-1-proteinase inhibitor (alpha 1-PI). Stable HBK inhibitor complex was detected at 92 K by immunoblotting employing anti-HUK as a probe. Anti alpha 1-PI probes did not demonstrate the 92 K complex under identical conditions, raising the possibility of an additional co-purifying protein involved in HBK binding. alpha 1-PI antigenic and activity levels were measured in asthmatic bronchoalveolar lavage (BAL) fluid. In only a single sample of the six examined was alpha 1-PI activity detected. In two of the remaining five samples, low levels of alpha 1-PI antigen were present which were functionally inactive. In the BAL fluid containing alpha 1-PI activity, progressive functional inhibition of kininogenase activity correlating with HBK inhibitor complex formation occurred during BAL fluid incubation. In contrast, BAL fluid lacking alpha 1-PI activity failed to show progressive kininogenase inhibition or complex formation under identical conditions. In all experiments, the time course of HBK inhibitor interaction was markedly prolonged, requiring 150-min co-incubation with either NHP or the alpha 1-PI preparation for greater than 80% inhibition of function and near maximal complex formation. The slow rate of inhibition of HBK may allow for its continued activity and kinin generation in the airways of asthmatic subjects.     

High-molecular weight kininogen is present in cultured human endothelial cells: localization, isolation, and characterization

The presence of high-molecular weight (mol wt) kininogen was demonstrated in cultured human endothelial cells derived from the umbilical cord by immunofluorescence techniques. Cultured human endothelial cells contain 58 +/- 11 ng (n = 16) high-mol wt kininogen/10(6) cells as determined by an enzyme-linked immunosorbent assay (ELISA) specific for high-mol wt kininogen. High-mol wt kininogen was isolated from cultured human endothelial cells by immunoaffinity chromatography. Nonreduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that endothelial cell high-mol wt kininogen consisted of five protein bands with mol wts of 95,000, 85,000, 65,000, 46,000, and 30,000 daltons. Immunoblotting of the endothelial cell high-mol wt kininogen by using specific antisera against the heavy and light chain indicated that the 95,000-, 85,000-, and 65,000-dalton bands consisted of the heavy and light chain whereas the 46,000- and 30,000-dalton bands reacted only with the anti-light chain antiserum. Immunoprecipitation studies performed with lysed, metabolically labeled endothelial cells and monospecific antisera directed against high-mol wt kininogen suggested that high-mol wt kininogen is not synthesized by the endothelial cells. Endothelial cells cultured in high-mol wt kininogen-free medium did not contain high-mol wt kininogen. These studies indicate that endothelial cell high-mol wt kininogen was proteolytically cleaved in the culture medium and subsequently internalized by the endothelial cells. Binding and internalization studies performed with 125I-labeled, proteolytically cleaved, high-mol wt kininogen showed that endothelial cells can indeed bind and internalize proteolytically cleaved high-mol wt kininogen in a specific and saturable way.     

Immunocytochemical analysis of tissue kallikrein and the kinin moiety in rheumatoid synovial fluid neutrophils

Polymorphonuclear leucocytes (PMNs) from the synovial fluid of patients with rheumatoid arthritis (RA) showed reduced tissue kallikrein and kinin immunoreactivity in comparison with blood PMNs from healthy individuals as judged visually using confocal microscopy. Similarly, synovial fluid PMNs exhibited reduced tissue kallikrein immunoreactivity as compared with blood PMNs from the same RA patients. Blood PMNs stimulated to degranulate in vitro also displayed less immunostaining for tissue kallikrein and kinin than non-stimulated PMNs. By contrast, no difference in kininogen immunostaining was detected between RA synovial fluid PMNs and blood PMNs from healthy people. It is considered that the results support the hypothesis that tissue kallikrein, released from the granules of RA synovial fluid PMNs, cleaves the kinin moiety from multifunctional kininogen protein on the surface of the PMNs.      

Plasma kallikrein/kinin system: a revised hypothesis for its activation and its physiologic contributions

Recent studies indicate that assembly of high molecular weight kininogen on its multiprotein receptor allows for prekallikrein activation. On endothelial cells, factor XII activation is secondary to prekallikrein activation and amplifies it. The immediate consequence of plasma prekallikrein activation is the cleavage of high molecular weight kininogen (HK) with liberation of bradykinin. Cleaved high molecular weight kininogen is antiangiogenic. Bradykinin stimulates tPA liberation and nitric oxide formation. In addition, formed plasma kallikrein promotes single-chain urokinase activation and subsequent plasminogen activation. Kininogens and their breakdown products also are antithrombins. The angiotensin converting enzyme breakdown product of bradykinin prevents canine coronary thrombosis. The author presents a new hypothesis for physiologic assembly and activation of the plasma kallikrein/kinin system and discusses its influence on vascular biology.     

The contact activation mechanism in human plasma: activation induced by dextran sulfate

Incubation of normal human plasma with dextran sulfate for 7 min at 4 degrees C generates kallikrein amidolytic activity. No kallikrein activity is generated in factor XII or prekallikrein-deficient plasma and only small amounts (8%) in high molecular weight (HMW) kininogen- deficient plasma. Addition of specific antisera directed against prekallikrein or HMW kininogen to normal plasma blocked the generation of kallikrein activity by dextran sulfate. Thus, factor XII, prekallikrein, and HMW kininogen are essential components for optimal activation of prekallikrein. The role of limited proteolysis in the activation of prekallikrein induced by dextran sulfate was studied by adding 125I-prekallikrein to plasma. The generation of kallikrein activity paralleled the proteolytic cleavage of prekallikrein as judged on SDS gels in the presence of reducing agents. The same cleavage fragments were observed as obtained by activation of purified prekallikrein by beta-factor-XIIa. Addition of 131I-HMW kininogen and 125I-factor XII or 131I-HMW kininogen and 125I-prekallikrein to normal plasma followed by activation with dextran sulfate and analysis on SDS gels indicated that the observed cleavage of prekallikrein and HMW kininogen is fast compared to the observed cleavage of factor XII, which is much slower and less extensive. During the first minutes of incubation of normal plasma with dextran sulfate, mainly alpha-factor- XIIa is formed. During prolonged incubation, beta-factor-XIIa is also formed.     

Tissue kallikrein elicits cardioprotection by direct kinin b2 receptor activation independent of kinin formation

Tissue kallikrein exerts various biological functions through kinin formation with subsequent kinin B2 receptor activation. Recent studies showed that tissue kallikrein directly activates kinin B2 receptor in cultured cells expressing human kinin B2 receptor. In the present study, we investigated the role of tissue kallikrein in protection against cardiac injury through direct kinin B2 receptor activation using kininogen-deficient Brown Norway Katholiek rats after acute myocardial infarction. Tissue kallikrein was injected locally into the myocardium of Brown Norway Katholiek rats after coronary artery ligation with and without coinjection of icatibant (a kinin B2 receptor antagonist) and N(omega)-nitro-L-arginine methylester (an NO synthase inhibitor). One day after myocardial infarction, tissue kallikrein treatment significantly improved cardiac contractility and reduced myocardial infarct size and left ventricle end diastolic pressure in Brown Norway Katholiek rats. Kallikrein attenuated ischemia-induced apoptosis and monocyte/macrophage accumulation in the ischemic myocardium in conjunction with increased NO levels and reduced myeloperoxidase activity. Icatibant and N(omega)-nitro-L-arginine methylester abolished kallikrein's effects, indicating a kinin B2 receptor NO-mediated event. Moreover, inactive kallikrein had no beneficial effects in cardiac function, myocardial infarction, apoptosis, or inflammatory cell infiltration after myocardial infarction. In primary cardiomyocytes derived from Brown Norway Katholiek rats under serum-free conditions, active, but not inactive, kallikrein reduced hypoxia/reoxygenation-induced apoptosis and caspase-3 activity, and the effects were mediated by kinin B2 receptor/nitric oxide formation. This is the first study to demonstrate that tissue kallikrein directly activates kinin B2 receptor in the absence of kininogen to reduce infarct size, apoptosis, and inflammation and improve cardiac performance of infarcted hearts.     

Interactions of plasma kallikrein and C1-s with normal and dysfunctional C1(-)-inhibitor proteins from patients with hereditary angioneurotic edema: analytic gel studies

Purified preparations of normal C1(-)-inhibitor (C1(-)-INH) formed high mol wt complexes with plasma kallikrein that were stable during sodium dodecyl sulfate (SDS)-gel electrophoresis, but most of the dysfunctional C1(-)-INH proteins isolated from plasma of patients with type II hereditary angioneurotic edema (HANE) did not. Two of eight dysfunctional C1(-)-INH proteins were cleaved to lower mol wt forms that were not seen following the reaction of normal C1(-)-INH with equimolar amounts, or less, of plasma kallikrein. Only the higher mol wt component of normal C1(-)-INH (106,000 mol wt) appeared to form a stable complex with the plasma kallikrein, whereas both the 106,000 and 96,000 mol wt forms made stable complexes with C1-s. When a preparation of normal C1(-)-INH containing a homogeneous single band of C1(-)-INH was exposed to C1-s or kallikrein, a "doublet" form evolved in which the heaviest band was in the original position of native C1(-)-INH; C1- s cleavage provided a second band of 96,000; and cleavage by kallikrein, a second band of 94,000 mol wt. We conclude that dysfunctional C1(-)-INH proteins from plasma of persons with type II hereditary angioneurotic edema have impaired interactions with plasma kallikrein and are heterogeneous with respect to these interactions. Moreover, the requirements for the formation of stable complexes between normal C1(-)-INH and plasma kallikrein differed from those for stable complex formation with C1-s. The doublet form of C1(-)-INH, which purified preparations frequently demonstrate, may be due to prior cleavage by C1-s or kallikrein.     

Purification of human pancreatic kallikrein and organ-specificities of human glandular kallikreins

Human pancreatic kallikrein (H. Panc. K.) was purified from human pancreas by serial liquid chromatographies. The final preparation had a specific activity of 9.2 AU/A280 (AU: amidase unit for H-Pro-Phe-Arg-MCA) and its N-terminal sequence coincided with the reported sequence determined from cloned cDNA analysis. In HPLC (gel filtration), one symmetrical peak corresponding to a molecular weight of 48,000 was obtained. In SDS-PAGE without 2-mercaptoethanol, one band corresponding to a molecular weight of 52,000 was obtained. Protease inhibitor specificities of H. Panc. K. were the same as those of human urinary kallikrein (HUK) and hog pancreatic kallikrein (hog Panc. K.), while anti-HUK rabbit antibody inhibited the activities of H. Panc. K. and HUK, but not that of hog Panc. K. From the analysis of affinity for concanavalin A and erythroagglutinating phytohemagglutinin, the carbohydrate parts of H. Panc. K. are relatively rich in bi-(or multi-) antennary complex type sugar chains with bisecting GlcNAc compared with those of human salivary kallikrein and HUK. These findings will be a help to clarify the physiological and pathophysiological roles of H. Panc. K. in the pancreas and pancreatic diseases, especially in acute pancreatitis.     

Plasma Kallikrein and Diabetic Macular Edema

Recent proteomic studies have identified components of the kallikrein kinin system, including plasma kallikrein, factor XII, and kininogen, in vitreous obtained from individuals with advanced diabetic retinopathy. In rodent models, activation of plasma kallikrein in vitreous increases retinal vascular permeability; whereas inhibition of the kallikrein kinin system reduces retinal leakage induced by diabetes and hypertension. These findings suggest that intraocular activation of the plasma kallikrein pathway may contribute to excessive retinal vascular permeability that can lead to diabetic macular edema. The kallikrein kinin system contains two separate and independently regulated serine proteases that generate bradykinin peptides: plasma kallikrein and tissue kallikrein. Tissue kallikrein is expressed in the retina and ciliary body, where it has been implicated in exerting autocrine or paracrine effects via bradykinin receptors that are colocalized in these tissues. Emerging evidence suggests that plasma kallikrein inhibitors may provide a new therapeutic opportunity to reduce retinal vascular permeability.