Purification and characterization of human Factor II

Effect of anticoagulation with citrate versus heparin on the adsorption of coagulation factors to blood purification resins with different charge

In liver failure, hydrophobic toxins accumulate in the blood circulation. To support hepatic function, extracorporeal blood purification systems have been developed, in which both cationic and neutral adsorbents are used to remove albumin-bound metabolites from blood. An issue of these systems is the additional removal of coagulation factors containing negatively charged γ-carboxyglutamate (Gla) domains, which, in physiological conditions, are shielded by calcium ions. We hypothesized that complexation of calcium ions by citrate leads to exposure of negative Gla domains, resulting in their binding to the positively charged adsorbents. The data presented here confirm that the binding of coagulation factors containing Gla domains to positively charged polymers is enhanced in the presence of citrate as compared to heparin. This effect increased with increasing charge density of the polymer and has important implications for the clinical application of positively charged polymers.

Prothrombin activation on the activated platelet surface optimizes expression of procoagulant activity

Effective hemostasis relies on the timely formation of α-thrombin via prothrombinase, a Ca(2+)-dependent complex of factors Va and Xa assembled on the activated platelet surface, which cleaves prothrombin at Arg271 and Arg320. Whereas initial cleavage at Arg271 generates the inactive intermediate prethrombin-2, initial cleavage at Arg320 generates the enzymatically active intermediate meizothrombin. To determine which of these intermediates is formed when prothrombin is processed on the activated platelet surface, the cleavage of prothrombin, and prothrombin mutants lacking either one of the cleavage sites, was monitored on the surface of either thrombin- or collagen-activated platelets. Regardless of the agonist used, prothrombin was initially cleaved at Arg271 generating prethrombin-2, with α-thrombin formation quickly after via cleavage at Arg320. The pathway used was independent of the source of factor Va (plasma- or platelet-derived) and was unaffected by soluble components of the platelet releasate. When both cleavage sites are presented within the same substrate molecule, Arg271 effectively competes against Arg320 (with an apparent IC(50) = 0.3μM), such that more than 90% to 95% of the initial cleavage occurs at Arg271. We hypothesize that use of the prethrombin-2 pathway serves to optimize the procoagulant activity expressed by activated platelets, by limiting the anticoagulant functions of the alternate intermediate, meizothrombin.

Evaluation of expanded bed adsorption chromatography for extraction of prothrombin complex from Cohn Supernatant I

This study evaluated the feasibility of substituting expanded bed adsorption (EBA) chromatography for an existing chromatographic purification process for the isolation of prothrombin complex concentrate (PCC) from Cohn Supernatant I. The EBA chromatography (Streamline) resins were compared to the current DEAE-cellulose resin for the extraction of PCC from Cohn SNI. EBA chromatography resins efficiently bound PCC from Cohn SNI at a significantly higher flow rate of up to 300 cm/h compared to 30 cm/h for the current DEAE-cellulose process. Composition and yield of the recovered PCC reflected the elution conditions used. The results indicate that EBA chromatography could be used to efficiently produce PCC comparable to existing products.

Antiprothrombin antibodies are associated with pregnancy loss in patients with the antiphospholipid syndrome

OBJECTIVE

To document the clinical association between the history of pregnancy loss in patients with the diagnosis of primary or secondary antiphospholipid syndrome (APS) and the presence of different antiprothrombin antibody subtypes [immunoglobulin G (IgG), IgM and IgA] in a cohort of patients with APS.

METHODS

Records of 170 female patients with primary APS, or APS secondary to systemic lupus erythematosus (SLE) or secondary to other autoimmune diseases were studied.

RESULTS

In female APS patients with IgG antiprothrombin antibodies (n = 105) significant associations to pregnancy loss (p < 0.0001), early pregnancy loss (p < 0.0001) and a negative association to thrombocytopenia (p < 0.01) could be identified. In the group of patients with IgG antiprothrombin antibodies and at least one pregnancy (n = 84) a significant association with pregnancy loss (p < 0.005) and especially with early pregnancy loss (p < 0.0001) was demonstrated. No association with other immunoglobulin subtypes of antiprothrombin antibodies could be documented. In the subgroup of patients with primary APS and at least one pregnancy in the history, pregnancy loss (p < 0.005) and early pregnancy loss (p < 0.0001) were found to be highly associated with the presence of IgG antiprothrombin antibodies. IgG antiprothrombin antibodies represent the highest independent risk factor for pregnancy loss with an odds ratio of 4.5. There was no statistically significant association with venous or arterial thrombosis in all IgG antiprothrombin antibody positive patients.

CONCLUSION

The results of this study document the association of IgG antiprothrombin antibodies with pregnancy loss and in particular early pregnancy loss in a large and well-characterized cohort of patients. We would recommend routine testing for antiprothrombin antibodies in young female patients with APS.

Activation of human prothrombin by arginine-specific cysteine proteinases (Gingipains R) from porphyromonas gingivalis

The effect of 95- (HRgpA) and 50-kDa gingipain R (RgpB), arginine-specific cysteine proteinases from periodontopathogenic bacterium Porphyromonas gingivalis on human prothrombin activation was investigated. Each enzyme released thrombin from prothrombin in a dose- and time-dependent manner with the former enzyme, containing adhesion domains, being 17-fold more efficient than the single chain RgpB. A close correlation between the generation of fibrinogen clotting activity and amidolytic activity indicated that alpha-thrombin was produced by gingipains R, and this was confirmed by SDS-polyacrylamide gel electrophoresis, thrombin active site labeling, and amino-terminal sequence analysis of prothrombin digestion fragments. Significantly, the catalytic efficiency of HRgpA to generate thrombin (k(cat)/K(m) = 1.2 x 10(6) m(-)1 s(-)1) was 100-fold higher than that of RgpB (k(cat)/K(m) = 1.2 x 10(4) m(-)1 s(-)1). The superior prothrombinase activity of HRgpA over RgpB correlates with the fact that only the former enzyme was able to clot plasma, and kinetic data indicate that prothrombin activation can occur in vivo. At P. gingivalis-infected periodontitis sites HRgpA may be involved in the direct production of thrombin and, therefore, in the generation of prostaglandins and interleukin-1, both have been found to be associated with the development and progression of the disease. Furthermore, by taking into account that the P. gingivalis bacterium has been immunolocalized in carotid atherosclerotic plaques at thrombus formation sites (Chiu, B. (1999) Am. Heart J. 138, S534-S536), our results indicate that bacterial proteinases may potentially participate in the pathogenesis of cardiovascular disease associated with periodontitis.

Thrombin inhibition by HCII in the presence of elastase-cleaved HCII and thrombin-HCII complex

The rate of thrombin inhibition by heparin cofactor II (HCII) is facilitated by heparin or dermatan sulfate in vitro. The distributions of these glycosaminoglycans (GAGs) in vivo are not the same; heparin-like substance is rich on the surface of endothelial cells and dermatan sulfate is relatively dominant in the extravascular region. When inflammation takes place, at least two other possible existent forms of HCII, the complexed form with thrombin and the cleaved form by leukocyte elastase, are assumed to be present at relatively high concentrations in a local circumstance. We examined the interactions of HCII with the two forms of HCII on thrombin inhibition in the presence of the GAGs. By HCII in complex with thrombin or cleaved by leukocyte elastase, the affinity of HCII moiety for heparin increases and that for dermatan sulfate decreases. The two forms possibly occur at relatively high concentrations in a local pathological situation, although the heparin cofactor activity for thrombin inhibition by HCII decreases and dermatan sulfate determines the cofactor activity. These results indicate efficient thrombin inhibitory activity of HCII in the extravascular region.

Separation of human vitamin K-dependent coagulation proteins using hydrophobic interaction chromatography

A rapid and simple method was developed to separate human vitamin K-dependent plasma proteins from each other, yielding virtually homogeneous pools. The purification technique is based on the single use of hydrophobic interaction chromatography, starting from prothrombin concentrate (PC or DEFIX, also termed factor IX concentrate) as initial material. Phenyl-sepharose HP demonstrated optimal separation by comparing several hydrophobic resins as well as resins used in standard procedures like immobilised heparin and Cibacron blue. Under ideal conditions, factor X could be separated in a single step as well as prothrombin. Factor IX co-eluted with other minor proteins. Focus was given only on these three proteins due to their relative abundance. Complete separation of all proteins present in the starting material was achieved by MonoQ anion-exchange chromatography following the phenyl-sepharose run. The resulting purified material could be demonstrated to be of equal or higher purity than using described methods. This strategy employing hydrophobic interaction chromatography for blood macromolecules could be of immense value for purifying the human vitamin K-dependent proteins and represents a considerable simplification over other purification schemes. It not only involves minimal sample handling but also can be readily up-scaled and is a cost-efficient alternative.

Thrombin mutants with altered enzymatic activity have an impaired mitogenic effect on mouse fibroblasts and are inefficient modulators of stellation of rat cortical astrocytes

We produced recombinant human thrombin mutants to investigate the correlation between the thrombin enzyme and mitogenic activity. Single amino acid substitutions were introduced in the catalytic triad (H43N, D99N, S205A, S205T), in the oxy-anion binding site (G203A) and in the anion binding exosite-1 region (R73E). Proteins were produced as prethrombin-2 mutants secreted in the culture medium of DXB11-derived cell lines. All mutants were activated by ecarin to the corresponding thrombin mutants; the enzymatic activity was assayed on a chromogenic substrate and on the procoagulant substrate fibrinogen. Mutations S205A and G203A completely abolished the enzyme activity. Mutations H43N, D99N and S205T dramatically impaired the enzyme activity toward both substrates. The R73E mutation dissociated the amidolytic activity and the clotting activity of the protein. The ability of thrombin mutants to induce proliferation was investigated in NIH3T3 mouse fibroblasts and rat cortical astrocytes. The ability of the thrombin mutants to revert astrocyte stellation was also studied. The mitogenic activity and the effect on the astrocyte stellation of the thrombin mutants correlated with their enzymatic activity. Furthermore the receptor occupancy by the inactive S205A mutant prevented the thrombin effects providing strong evidence that a proteolytically activated receptor is involved in cellular responses to thrombin.

Selective inhibition of factor Xa in the prothrombinase complex by the carboxyl-terminal domain of antistasin

Studies of antistasin, a potent factor Xa inhibitor with anticoagulant properties, were performed wherein the properties of the full-length antistasin polypeptide (ATS-119) were compared with the properties of forms of antistasin truncated at residue 116 (ATS-116) and residue 112 (ATS-112). ATS-119 was 40-fold more potent than ATS-112 in prolonging the activated partial thromboplastin time (APTT), whereas ATS-119 inhibited factor Xa 2.2-fold less avidly and about 5-fold more slowly than did ATS-112. The decreased reactivity of ATS-119 suggests that the carboxyl-terminal domain of ATS-119 stabilizes an ATS conformation with a reduced reactivity toward factor Xa. The observation that calcium ion increases the reactivity of ATS-119 but not that of ATS-112 suggests that calcium ion may disrupt interactions involving the carboxyl terminus of ATS-119. Interestingly, ATS-119 inhibited factor Xa in the prothrombinase complex 2-6-fold more potently and 2-3-fold faster than ATS-112. These differences in affinity and reactivity might well account for the greater effectiveness of ATS-119 in prolonging the APTT and suggest that the carboxyl-terminal domain of ATS-119 disrupts interactions involving phospholipid, factor Va, and prothrombin in the prothrombinase complex. The peptide RPKRKLIPRLS, corresponding to the carboxyl domain of ATS-119 prolonged the APTT and inhibited prothrombinase-catalyzed processing of prothrombin, but it failed to inhibit the catalytic activity of isolated factor Xa. Thus, this novel inhibitor appears to exert its inhibitory effects at a site removed from the active site of factor Xa.

Large-scale preparation of human thrombin: polyethylene glycol potentiates the factor Xa-mediated activation of prothrombin

We investigated the ability of polyethylene glycol 4000 to accelerate thrombin generation in a mixture of prothrombin and factor X at concentrations of 1-30%. In the presence of 5 mM of CaCl2, polyethylene glycol 4000 promoted prothrombin activation at concentrations above 1%. The peak of activation was seen at levels of 14 and 20% of polyethylene glycol 4000. The effect of the polyethylene glycol was remarkably dependent on its molecular weight; molecular weights greater than 2000 were required for accelerating thrombin generation. Under optimal conditions, polyethylene glycol 4000, in the presence of CaCl2, promoted conversion of all of the prothrombin into thrombin and its derivatives. We conclude that polyethylene glycol 4000, at concentrations ranging from 14 to 20%, effectively accelerates thrombin generation in the presence of 5 mM of CaCl2. This new method for preparing thrombin is based on the use of polyethylene glycol 4000 and CaCl2 and is applicable to the manufacture of thrombin.

Biospecific interactions of Vitamin K-dependent factors with phospholipid-like polystyrene derivatives. Part I: Factor II

Phosphorylated polystyrene derivatives with different compositions in phosphate groups were shown to be either recognized as phospholipidic or as DNA-like surfaces by antibodies from Systemic Lupus Erythematosus patients. In order to check whether these polymers were able to interact with Vitamin K-dependent coagulation factors, phosphorylated resins of various compositions in phosphate groups were assessed with regard to their interactions with Factor II, one of the Vitamin K-dependent factors. These studies were performed either in the presence or the absence of calcium ions, and with or without albumin precoating of the polymers. The results show that the affinity of the protein for the polymer is increased in the presence of calcium ions and depends on the composition of the polymer. The protein-polymer interactions involve the formation of binary or ternary complexes and the domains of predominance of these complexes were determined as a function of the calcium ion concentration in the assay. This allowed us to propose optimal conditions for Factor II purification by highly specific liquid chromatography using phosphorylated polystyrene resins of given compositions as stationary phases.

Large-scale production and properties of immunoaffinity-purified human activated protein C concentrate

Activated protein C (APC) is a highly specific serine proteinase which functions as an important naturally occurring antithrombotic enzyme. APC also has anti-inflammatory properties. We have developed a large-scale process for the production of APC for therapeutic use starting with cryoprecipitate-poor human plasma. This report describes the process, its performance at the pilot plant scale, and the characteristics of immunoaffinity-purified human APC concentrate referred to as APC (human). The process consists of three chromatographic steps, an enzymatic conversion step, and incorporates a solvent/detergent treatment step for the inactivation of lipid-enveloped viruses. Solvent/detergent was shown to rapidly inactivate spiked HIV-1, as well as three marker viruses to nondetectable levels under process conditions. The immunoaffinity-purified protein C (PC) intermediate was enriched 13,600-fold over plasma and had a specific activity of 231 U/mg. The overall yield of the process following enzymatic conversion of the PC intermediate to APC and its processing by anion exchange chromatography was 36%. APC (human) was shown to be highly purified, functional and stable.

Hepsin, a putative membrane-associated serine protease, activates human factor VII and initiates a pathway of blood coagulation on the cell surface leading to thrombin formation

Previous studies have shown that hepsin is a putative membrane-associated serine protease that is required for cell growth (Torres-Rosado, A., O'Shea, K. S., Tsuji, A., Chou, S.-H., and Kurachi, K. (1993) Proc. Natl. Acad. Sci. U.S. A. 90, 7181 7185). In the present study, we have transfected baby hamster kidney (BHK) cells with a plasmid containing the cDNA for human hepsin and examined these cells for their ability to activate several blood coagulation factors including factors X, IX, VII, prothrombin, and protein C. Little, if any, proteolytic activation of factors X, IX, prothrombin, or protein C was observed when these clotting factors were incubated with hepsin-transfected cells. On the other hand, hepsin-transfected cells proteolytically activated significant concentrations of human factor VII in a time- and calcium-dependent manner, whereas essentially no activation of factor VII was observed in BHK cells transfected with plasmid lacking the cDNA for hepsin. The factor VII activating activity in the hepsin-transfected BHK cell line was confined exclusively to the total membrane fraction and was inhibited > 95% by antibody raised against a fusion protein consisting of maltose-binding protein and the extracellular domain of human hepsin. An active site factor VII mutant, S344A factor VII, was cleaved as readily as plasma-derived factor VII by hepsin-transfected cells, indicating that factor VII was not converted to factor VIIa autocatalytically on the cell surface. In contrast, an activation cleavage site factor VII mutant, R152E factor VII, was not cleaved by hepsin-transfected cells, suggesting that factor VII and S344A factor VII were activated on these cells by cleavage of the Arg152-Ile153 peptide bond. In the copresence of factor VII and factor X, hepsin-transfected BHK cells supported the formation of factor Xa. In addition, in the copresence of factor VII, factor X, and prothrombin, hepsin-transfected BHK cells supported the formation of thrombin. These results strongly suggest that membrane-associated hepsin converts zymogen factor VII to factor VIIa, which in turn, is capable of initiating a coagulation pathway on the cell surface that ultimately leads to thrombin formation.

Molecular mapping of the heparin-binding exosite of thrombin

Thrombin contains electropositive patches at opposite poles of the molecule which represent potential exosites for the binding of macromolecular ligands. The function of anion-binding exosite I, the fibrin(ogen) recognition site, has been well described. Anion-binding exosite II, located near the carboxyl terminus of the molecule, has been proposed to bind heparin on the basis of chemical modification studies. To define the functional heparin-binding site on thrombin, purified recombinant alpha-thrombins were prepared with glutamic acid substitution for selected basic amino acid residues in exosite II or exosite I. Heparin affinity was assessed by NaCl gradient elution from heparin-agarose, and second-order rate constants for inhibition by antithrombin III were determined in the absence and presence of heparin. Affinity for heparin-agarose was reduced markedly by selected mutations in exosite II (R89E, R245E, K248E, and K252E, numbered from the amino terminus of the B chain) but not by other mutations in exosite II (K174E, K247E) or by mutations in exosite I (R68E, K154E). All recombinant thrombins had similar rate constants for inhibition by antithrombin III without heparin. However, affinity for heparin-agarose correlated directly with the rate of inhibition by antithrombin III with heparin. These results demonstrate that selected mutations in anion-binding exosite II define a functional heparin-binding site and support the template mechanism of heparin action.

Intact platelet membranes, not platelet-released microvesicles, support the procoagulant activity of adherent platelets

The possibility that platelets release microvesicles on adherence to either von Willebrand factor (vWf) or collagen was examined by flow cytometry analysis of the supernatant above layers of adherent platelets. No microvesicle release was detected as a result of adherence to vWf or to collagen, a known platelet agonist. Approximately 8% of the total platelet mass was released as microvesicles after thrombin stimulation of the vWf- or collagen-adherent platelets. A larger portion of the vWf-adherent platelet membranes (approximately 21%) was released as microvesicles subsequent to platelet stimulation with the nonphysiological agonist calcium ionophore A23187. Calpeptin, a calpain inhibitor, had no effect on microvesicle release, suggesting that calpain proteolysis of platelet cytoskeletal proteins was not responsible for microvesicle shedding under the conditions studied. Examination of the vWf-adherent platelets by scanning electron microscopy showed that virtually no microvesicles bound to exposed vWf multimers. No microvesicle binding to the adherent platelets was observed, indicating that the majority of the microvesicles were shed from the platelet and vWf surface on platelet activation. The ability of the microvesicle population to support procoagulant activity was measured with a prothrombinase activity assay and was compared with the activity supported by the adherent platelet membranes. More than 85% of the total prothrombinase activity remained associated with the adherent platelet membranes, both for unstimulated platelets and platelets stimulated with physiological agonists. Furthermore, the residual activity found in the buffer fraction containing detached platelets and any released microvesicles could be attributed to the detached platelets. No activity could be attributed to the microvesicles, as thrombin stimulation of either vWf-or collagen-adherent platelets did not promote increased procoagulant activity relative to the unstimulated adherent platelets, even though microvesicle release was detected as a result of agonist addition. Neither full platelet activation nor microvesicle shedding played an essential role in generating procoagulant activity in the adherent platelet system.

Non-specific effects of aquaMEPHYTON (vitamin K1) on prothrombin expression in human hepatoblastoma (HepG2) cells

In order to determine the effects of vitamin K1 on prothrombin production, we have treated cultures of human hepatoblastoma cells with an aqueous colloidal suspension of vitamin K1. Dose-response analysis demonstrated increases in secreted prothrombin antigen levels ranging from 3 to 3.7-fold over controls. Time-course analysis demonstrated increases in secreted prothrombin antigen levels over controls up to 6 hours of treatment. Between 6 and 24 hours, secreted prothrombin antigen levels increased at a rate parallel to controls. Vitamin K1 treatment also resulted in a parallel increase in total secreted protein levels. Prothrombin mRNA size (approximately 2.1 kb) and levels (ranging from 390-480 prothrombin mRNA molecules per cell) were determined by Northern and quantitative solution hybridization analysis, respectively, and were unaffected by vitamin K1 treatment. The increases in secreted prothrombin antigen levels most likely result from non-specific effects of vitamin K1 or agents used to emulsify vitamin K1 on protein release from HepG2 cells.

Activation of human factor VII by the prothrombin activator from the venom of Oxyuranus scutellatus (Taipan snake)

The crude venom of Oxyuranus scutellatus (Taipan snake) was found to cleave single-chain human factor VII to yield a two-chain molecule indistinguishable from authentic factor VIIa by SDS-polyacrylamide gel electrophoresis. A protease that activates factor VII was purified from this venom by a combination of gel permeation and ion-exchange chromatography. Characterization of the venom factor VII activator revealed its apparent identity with the Oxyuranus scutellatus prothrombin activator. The purified venom prothrombin activator was observed to activate factor VII by limited proteolysis in a reaction that was greatly potentiated by calcium and phospholipids (75% phosphatidyl choline/25% phosphatidylserine). Treatment of the venom protease with 0.8 M NaSCN weakly inhibited its ability to activate factor VII indicating that, in contrast to prothrombin activation, the factor Va-like component of this oligomeric enzyme complex was not essential for the activation of factor VII.

Single amino acid substitutions dissociate fibrinogen-clotting and thrombomodulin-binding activities of human thrombin

Thrombin is a serine protease that acts as a procoagulant by clotting fibrinogen and activating platelets and as an anticoagulant by activating protein C in a thrombomodulin-dependent reaction. Fibrinogen and thrombomodulin bind competitively to an anion-binding exosite on thrombin. We prepared recombinant normal human thrombin and mutant thrombins with single amino acid substitutions in order to localize and distinguish the fibrinogen- and thrombomodulin-binding sites. Normal and mutant thrombins had similar amidolytic activity. Thrombin K52E had approximately 2.5-fold increased protein C-activating activity but only approximately 17% of normal fibrinogen-clotting activity. Thrombin R70E had normal fibrinogen-clotting activity but only approximately 7% of normal protein C-activating activity. Thrombin R68E had markedly reduced activity in both assays. Decreased activation of protein C correlated with decreased binding affinity for thrombomodulin, and ability to activate platelets correlated directly with fibrinogen-clotting activity. These results demonstrate that thrombins with predominantly anticoagulant or procoagulant activity can be created by mutagenesis and that thrombomodulin- and fibrinogen-binding sites on thrombin may overlap but are not identical.

An o-toluidine method for detection of carbohydrates in protein hydrolysates

The o-toluidine high-performance thin-layer chromatography (HPTLC) method for detection of reducing sugars has been demonstrated to be a facile method for composition analysis of protein hydrolysates with a maximum sensitivity range of 50-100 pmol. The solution phase reaction of o-toluidine with reducing sugars has been previously used for spectrophotometric detection of glucose at 480-630 nm. In contrast, the heterogeneous reaction of o-toluidine with reducing sugars resolved by thin-layer chromatography produces chromophoric derivatives which have a broad absorbance at 295 nm. Detection of these chromophoric derivatives is achieved by uv diffuse reflectance scanning densitometry. It is demonstrated that detection limits of less than 10 ng can be achieved by using HPTLC plates and is therefore equal or more sensitive for some sugars than recently reported high-pressure liquid chromatography methods using amperometric or fluorescence detection.

Impairment of the protein C anticoagulant pathway in a patient with systemic lupus erythematosus, anticardiolipin antibodies and thrombosis

We have identified an inhibitor of the protein C anticoagulant pathway in the plasma of a patient with systemic lupus erythematosus and a history of recurrent deep vein thrombosis, fetal wastage, and seizures. The patient's plasma contained anticardiolipin antibodies as well as a weak lupus anticoagulant. Examination of this patient's plasma revealed normal levels of protein C and protein S antigen, normal levels of functional protein C, as well as essentially normal levels of every blood coagulation factor. In a modified prothrombin time assay, the activated protein C-mediated prolongation of the clotting time observed in normal plasma was not observed in this patient's plasma. Gel permeation chromatography of the patient's plasma revealed that the inhibitory material was a high molecular weight protein that coeluted with the IgM peak. The inhibitor did not appear to circulate as a complex with protein C, since the inhibitor could easily be separated from protein C during fractionation procedures, and did not interfere with the activation of protein C in plasma as assessed by a functional amidolytic assay. Our findings suggest that the recurrent thrombotic episodes observed in this patient may have occurred as a result of the patient's antiphospholipid antibody neutralizing specific phospholipids essential for the full expression of the anticoagulant activity of activated protein C.

Relative affinity of Ca(II) and Mg(II) ions for human and bovine prothrombin and fragment 1

Equilibrium dialysis results are presented for Ca(II) and Mg(II) ion binding to human and bovine prothrombin and fragment 1. Ca(II) ions bind cooperatively, Mg(II) does not.

Determination of magnesium binding to macromolecules

An equilibrium dialysis technique for examining magnesium binding to macromolecules is described. The technique is used to determine the binding constants of magnesium to human prothrombin. This procedure should be of great utility for many biochemical systems which exhibit magnesium affinity.

Purification of six human vitamin K-dependent proteins in a single chromatographic step using immunoaffinity columns

The major human vitamin K-dependent proteins were purified from plasma using immunoadsorbents made with antibodies specific for each protein. Monoclonal antibodies to Factor VII, Factor IX, Factor X, Protein C, and Protein S were prepared from mice immunized with isolated vitamin K-dependent antigens. Purified monoclonal antibodies and a purified burro polyclonal anti-prothrombin immunoglobulin were individually coupled to Sepharose and used in a tandem series of columns to purify each of the vitamin K-dependent proteins from eluates of barium citrate precipitates of plasma. The proteins were eluted from the columns by sodium thiocyanate and retained functional activity following dialysis. Prothrombin, Factor VII, Factor IX, Factor X and Protein C were essentially homogeneous as judged by NaDodSO4-PAGE; Protein S was isolated as a Protein S-C4b binding protein complex. These results indicate the utility of monoclonal antibody immunoadsorbents for purifying the human vitamin K-dependent proteins and represent a considerable simplification over other purification schemes.

Studies on the procoagulant activity of human amniotic fluid. I. Stability and coagulation factor requirements

A fraction of human amniotic fluid possessing procoagulant activity was purified 35-70 fold by gel filtration on Sepharose 4B. The activity eluted in the void volume indicating a particle size in excess of 5 X 10(6) daltons. The amniotic fluid factor (AFF) activity is stabilized on storage in the presence of Ca++ ions which could not be replaced by Mg++. Addition of phospholipids resulted in accelerated loss of activity. Steps taken to remove factor VII did not affect the activity, but factor X and V are required.

Inhibition of prothrombinase complex by plasma proteinase inhibitors

The rate of inactivation of human coagulation factor Xa by the plasma proteinase inhibitors antithrombin III and alpha 1-antitrypsin has been studied in the presence of the accessory components which constitute the prothrombinase complex. The rate of inactivation of factor Xa by antithrombin III was found to be decreased in the presence of phospholipid vesicles with high affinity for factor Xa. The second-order rate constant for the reaction fell from 6.21 X 10(4) to 3.40 X 10(4) M-1 min-1 in the presence of 20 microM phospholipid. Purified factor Va had no effect on the rate of inactivation of factor Xa in the absence of phospholipid. In the presence of phospholipid, factor Va increased the protective effect displayed by phospholipid, further reducing the rate constant to 2.20 X 10(4) M-1 min-1. The rate of inactivation of factor Xa by alpha 1-antitrypsin was unaffected under these conditions. Platelet-bound prothrombinase complex was formed by incubation of factor Xa with washed human platelets activated by a mixture of collagen and thrombin. The prothrombinase activity was inhibited by antithrombin III was a second-order rate constant of 0.85 X 10(4) M-1 min-1. This rate was obtained in both the presence and absence of exogenous factor Va. Platelet factor 3 vesicles, isolated from platelet aggregation supernatants, also formed prothrombinase complex in the presence of factor Va, and this was inhibited by antithrombin III at the same rate as the platelet-bound complex. There was no protection of the platelet-bound prothrombinase complex from inhibition by alpha 1-antitrypsin.

Origin of a fluorescence increase accompanying the limited proteolysis of fluorescein-labeled human prothrombin by Factor Xa

In a search for a probe which would report its proteolysis to thrombin, the human blood coagulation zymogen prothrombin was covalently labeled with fluorescein. Fluorescein isothiocyanate (FITC) and dichlorotriazinylaminofluorescein (DCTAF) both introduced approximately 1 molecule of dye, but labeling occurred at different locations, as FITC had no effect on clotting activity whereas DCTAF caused 95% inactivation. At pH 9.0 DCTAF, but not FITC, could induce labeling up to 4 mol/mol. All derivatives were activated normally by prothrombinase (the activating complex of Factor Xa, Factor V(a), Ca2+ and phospholipids), as indicated by the pattern of bands on SDS gel electrophoresis and an unaltered yield of activity toward a chromogenic substrate for thrombin. Upon undergoing this limited proteolysis, the most heavily labeled derivative showed a 40% increase in fluorescence of the fluorescein at 520 nm (lambda ex 480 nm). In contrast, the fluorescence of lightly labeled forms was more intense but increased by only 0-5% upon activation. The data suggest that the lower fluorescence of the most labeled form is due to an intramolecular quenching effect between the dye molecules on individual polypeptide chains that is partly relieved when activation occurs.

Permeability of rheumatoid and normal human synovium to specific plasma proteins

A method is described for the determination of the permeability of the blood-joint barrier to specific plasma proteins, using the ratio of protein concentration in synovial fluid to that in plasma. The inadequacy of the ratio per se as a direct index of permeability is discussed. Permeabilities are evaluated for the normal and rheumatoid human knee. Permeability increases in the rhematoid knee by approximately 6 times for the rheumatoid knee by approximately 6 times for albumin and over 40 times for macroglobulins. The effect of protein molecular dimensions upon permeability is analyzed. Permeability shows less dependence upon solute dimensions in the rheumatoid knee than in the normal knee, i.e., molecular selectivity is reduced. From these data and synovial morphology, a two-membrane model of the blood-joint barrier is developed. The relative contribution of the component intimal and endothelial layers to the total barrier is found to depend upon solute dimensions.

A simplified procedure for purification of human prothrombin, factor IX and factor X

A simplified procedure is described for the purification of prothrombin, Factor X and Factor IX in overall yields of 35-40% from pooled human plasma. The initial steps, which are common to prior purification techniques, include adsorption onto and elution from barium citrate, ammonium sulfate fractionation, and DEAE-Sephadex chromatography. The procedure differs from previous techniques in that the nest step, heparin-agarose chromatography, is carried out in a (sodium) citrate buffer, pH 7.5. These chromatographic conditions permit the separation of prothrombin, Factor X and Factor IX from each other, yielding fractions with apparent homogeneity in several electrophoretic systems. The additional chromatographic steps of earlier purification procedures are therefore unnecessary. The heaprin-agrarose column chromatographic conditions consistently resulted in the separation of human prothrombin in into two fractions in a ratio of approximately 4:1. Both fractions possess similar specific activity in a one stage prothrombin assay, and also activate at the same rate in a Factor Xa, Ca2+ and phospholipid system. Both fractions of prothrombin also comigrate in sodium dodecyl sulfate gel electrophoresis with an apparent Mr integral of 70,000.