Quantitation of prothrombin activation products in human urine

Crystallization of calcium oxalates is controlled by molecular hydrophilicity and specific polyanion-crystal interactions

To gain more insight into protein structure-function relationships that govern ectopic biomineralization processes in kidney stone formation, we have studied the ability of urinary proteins (Tamm-Horsfall protein, osteopontin (OPN), prothrombin fragment 1 (PTF1), bikunin, lysozyme, albumin, fetuin-A), and model compounds (a bikunin fragment, recombinant-, milk-, bone osteopontin, poly-L-aspartic acid (poly asp), poly-L-glutamic acid (poly glu)) in modulating precipitation reactions of kidney stone-related calcium oxalate mono- and dihydrates (COM, COD). Combining scanning confocal microscopy and fluorescence imaging, we determined the crystal faces of COM with which these polypeptides interact; using scanning electron microscopy, we characterized their effects on crystal habits and precipitated volumes. Our findings demonstrate that polypeptide adsorption to COM crystals is dictated first by the polypeptide's affinity for the crystal followed by its preference for a crystal face: basic and relatively hydrophobic macromolecules show no adsorption, while acidic and more hydrophilic polypeptides adsorb either nonspecifically to all faces of COM or preferentially to {100}/{121} edges and {100} faces. However, investigating calcium oxalates grown in the presence of these polypeptides showed that some acidic proteins that adsorb to crystals do not affect crystallization, even if present in excess of physiological concentrations. These proteins (albumin, bikunin, PTF1, recombinant OPN) have estimated total hydrophilicities from 200 to 850 kJ/mol and net negative charges from -9 to -35, perhaps representing a "window" in which proteins adsorb and coat urinary crystals (support of excretion) without affecting crystallization. Strongest effects on crystallization were observed for polypeptides that are either highly hydrophilic (>950 kJ/mol) and highly carboxylated (poly asp, poly glu), or else highly hydrophilic and highly phosphorylated (native OPN isoforms), suggesting that highly hydrophilic proteins strongly affect precipitation processes in the urinary tract. Therefore, the level of hydrophilicity and net charge is a critical factor in the ability of polypeptides to affect crystallization and to regulate biomineralization processes.

Face-specific binding of prothrombin fragment 1 and human serum albumin to inorganic and urinary calcium oxalate monohydrate crystals

OBJECTIVE

To compare the intracrystalline distributions of prothrombin fragment 1 (PTF1) and human serum albumin (HSA) within inorganic and urinary calcium oxalate (CaOx) monohydrate (COM) crystals and to determine whether binding of PTF1 can be explained by interactions between particular gamma-carboxyglutamic (Gla) residues and atomic arrays on individual faces of the COM crystal. MATERIALS AND METHODS COM: crystals were precipitated from inorganic solutions and ultrafiltered urine containing fluorescent HSA or PTF1 at different relative concentrations and examined by fluorescence microscopy. Accelrys Materials Studio and Discovery Studio were used to model the binding of PTF1 to the top, side and apical faces of the COM crystal.

RESULTS

PTF1 alone always adsorbed predominantly to the COM apical surfaces, while HSA bound principally to the side faces under inorganic conditions, but to the apical faces in urine. In the presence of each other, both proteins competed for adsorption to the apical faces, with attachment of PTF1 dominating over that of HSA. Modelling showed that urinary PTF1 had equal theoretical bonding potential for all three COM surfaces.

CONCLUSIONS

(i) Anisotropic inclusion of HSA and PTF1 into urinary and inorganic COM crystals results from their preferential binding to specific COM faces; (ii) the binding preference of HSA differs under inorganic and urinary conditions; (iii) preferential binding of PTF1 to the apical faces of COM is more complex than can be explained by interactions between Gla groups and surface atomic arrays; (iv) future studies of interactions between urinary proteins and stone mineral crystal surfaces should be performed in urine.

Intracrystalline urinary proteins facilitate degradation and dissolution of calcium oxalate crystals in cultured renal cells

We have previously proposed that intracrystalline proteins would increase intracellular proteolytic disruption and dissolution of calcium oxalate (CaOx) crystals. Chauvet MC, Ryall RL. J Struct Biol 151: 12-17, 2005; Fleming DE, van Riessen A, Chauvet MC, Grover PK, Hunter B, van Bronswijk W, Ryall RL. J Bone Miner Res 18: 1282-1291, 2003; Ryall RL, Fleming DE, Doyle IR, Evans NA, Dean CJ, Marshall VR. J Struct Biol 134: 5-14, 2001. The aim of this investigation was to determine the effect of increasing concentrations of intracrystalline protein on the rate of CaOx crystal dissolution in Madin-Darby canine kidney (MDCKII) cells. Crystal matrix extract (CME) was isolated from urinary CaOx monohydrate (COM) crystals. Cold and [14C]oxalate-labeled COM crystals were precipitated from ultrafiltered urine containing 0-5 mg/l CME. Crystal surface area was estimated from scanning electron micrographs, and synchrotron X-ray diffraction was used to determine nonuniform strain and crystallite size. Radiolabeled crystals were added to MDCKII cells and crystal dissolution, expressed as radioactive label released into the medium, was measured. Increasing CME content did not significantly alter crystal surface area. However, nonuniform strain increased and crystallite size decreased in a dose-response manner, both reaching saturation at a CME concentration of 3 mg/ and demonstrating unequivocally the inclusion of increasing quantities of proteins in the crystals. This was confirmed by Western blotting. Crystal dissolution also followed saturation kinetics, increasing proportionally with final CME concentration and reaching a plateau at a concentration of approximately 2 mg/l. These findings were complemented by field emission scanning electron microscopy, which showed that crystal degradation also increased relative to CME concentration. Intracrystalline proteins enhance degradation and dissolution of CaOx crystals and thus may constitute a natural defense against urolithiasis. The findings have significant ramifications in biomineral metabolism and pathogenesis of renal stones.

Glycosylation of prothrombin fragment 1 governs calcium oxalate crystal nucleation and aggregation, but not crystal growth

Urinary glycoproteins play an important role in the modulation of calcium oxalate crystallisation. In several cases, this has been attributed to glycosylation of the proteins as evidenced by urinary prothrombin fragment 1 where there is a correlation between sialylation and calcium oxalate kidney stone disease. In the present study, plasma-derived prothrombin fragment 1 (PTF1) was enzymatically modified in order to generate its asialo and aglyco forms. The parent glycoprotein and its two glycoforms were used in calcium oxalate crystallisation studies to assess the role of the carbohydrate moeity in PTF1's potent inhibitory activity. The glycans inhibited crystal aggregation and promoted crystal nucleation, but had no effect on crystal growth. The terminal sialic acid residues had a small effect on inhibition of crystal aggregation whereas they contributed significantly to promotion of nucleation. These results indicate that glycosylation of PTF1 governs calcium oxalate crystal nucleation and aggregation but it does not affect the protein's role in inhibiting crystal growth. Since promotion of nucleation and inhibition of aggregation are both regarded as protective mechanisms against calcium oxalate urinary stone formation, the kringle domain on which the glycans are located is implicated in PTF1's inhibitory activity. It is speculated that modifications in the glycosylation of urinary PTF1 in stone-formers may regulate its capacity to protect against calcium urolithiasis.

Calcium phosphate crystal-associated proteins: alpha-2-HS-glycoprotein, prothrombin fragment 1 and osteopontin

To study the inhibitory effects of calcium phosphate-associated proteins on calcium oxalate crystallization and urinary concentrations of proteins in people who form stones and healthy controls. From 60 L of urine from healthy men, calcium phosphate-associated proteins (alpha-2-HS-glycoprotein, prothrombin fragment 1 and osteopontin) were obtained. The effects of the proteins on calcium oxalate (CaOx) crystallization were studied with a mixed suspension mixed product removal system. To examine urinary concentrations of the proteins, urine samples were collected from 17 healthy subjects and 15 stone formers and analyzed using anion-exchange chromatography and an enzyme immunoassay. Prothrombin fragment 1 (PTF1) and osteopontin (OPN) had strong inhibitory effects on CaOx crystallization, while alpha-2-HS-glycoprotein had a mild inhibitory effect. Urinary concentrations of PTF1 and OPN were lower in stone formers than in healthy controls. Low urinary concentrations of PTF1 and OPN might be one of the reasons for stone formation.

Kringles of the plasminogen--prothrombin gene family share conformational epitopes with recombinant apolipoprotein (a): specificity of the fibrin-binding site

Monoclonal antibodies directed against recombinant apolipoprotein (a) (r-apo(a)) lacking plasminogen-like KIV-2 repeats were used to identify structurally related conformational epitopes in various members of the plasminogen-prothrombin gene family. A number of procedures including a fibrin-binding inhibition immunoassay and surface plasmon resonance studies were used. Two antibodies (A10.1 and A10.4) recognised common conformational structures in r-apo(a), prothrombin, factor XII, plasminogen and its tissue-type and urokinase-type activators. In contrast, two other antibodies recognised specifically an epitope comprising residues of the lysine-binding site (A10.2) or close to it (A10.5) and inhibited the fibrin-binding function of r-apo(a) (IC(50)=36 pmol/l and 9.76 nmol/l, respectively). Interestingly, these antibodies distinctly recognised the elastase-derived fragments of plasminogen K4 (A10.2) and K1+2+3 (A10.5) without affecting plasminogen binding to fibrin. These results suggest that highly conserved conformational regions are common to various proteins of the plasminogen-prothrombin gene family and are in agreement with the concept that these proteins constitute a monophyletic group derived from an ancestral gene.

A functional prothrombin gene product is synthesized by human kidney cells

gamma-carboxylated polypeptides were detected in the human kidney by immunohistochemistry with a monoclonal antibody (M3B) specific for gamma-carboxyglutamyl residues. An approximately 70-kDa gamma-carboxylated protein, subsequently identified as prothrombin, was isolated from the intracellular compartment of cultured human embryonic kidney (HEK293) cells by immunoaffinity chromatography on M3B-coupled resin. Immunohistochemical analyses demonstrated that prothrombin and another vitamin K-dependent protein, the growth arrest-specific protein 6, were detectable in human kidney. As in the liver, the kidney synthesizes prothrombin as a zymogen that can be cleaved by ecarin to an amidolytically active serine protease that is inhibited by hirudin. This demonstrates for the first time the de novo synthesis of a full-length, gamma-carboxylated, and functional prothrombin gene product by human kidney cells.

Changing concepts in the aetiology of renal stones

In the past two decades an increasing number of nephrolithiasis-related urinary proteins have been identified. This paper focuses on two of them, namely prothrombin fragment 1 and bikunin, members of the prothrombin and inter-alpha-trypsin inhibitor families of proteins, respectively. Besides their role as inhibitors of crystallization, these proteins are also involved in inflammation-mediated tissue repair. This is the basis for the concept that the response of renal tissue to injury might play an important role in the aetiology of kidney stones.

Inhibitory effect of calcium phosphate-associated proteins on calcium oxalate crystallization: alpha2-HS-glycoprotein, prothrombin-F1 and osteopontin

OBJECTIVE

To analyse urinary calcium phosphate- associated proteins and assess their inhibitory effects on calcium oxalate crystallization. Materials and methods Urine samples were collected over 24 h from five healthy men and calcium phosphate crystallization induced with NaOH solution. The bound proteins were separated on a cellulose column. To examine the effect of urinary calcium phosphate-associated proteins on calcium oxalate crystallization, 60 L of urine was collected from the healthy men. The effect of the separated fractions was studied in a mixed suspension/mixed product removal system.

RESULTS

The separated proteins were identified as alpha2-HS-glycoprotein, prothrombin fragment 1 and osteopontin. Prothrombin fragment 1 and osteopontin strongly inhibited the growth of calcium oxalate crystals in artificial urine.

CONCLUSION

alpha2-HS-glycoprotein, prothrombin fragment 1 and osteopontin selectively bound with calcium phosphate crystals in urine. Prothrombin fragment 1 and osteopontin in urine may strongly influence stone formation.

The prothrombin gene is expressed in the rat kidney: Implications for urolithiasis research

There is considerable interest in determining the role of prothrombin fragments, especially urinary prothrombin fragment 1 (UPTF1), in the pathogenesis of calcium oxalate (CaOx) urinary calculi. This fragment is present in abundance in the matrix of CaOx crystals generated in human urine in vitro and has also been detected in human urinary stones containing calcium. More recently, prothrombin gene expression has been reported in the human kidney. However, studies examining the renal biosynthesis of prothrombin or perhaps only its fragments during experimental lithogenesis, and in consequence, the role of UPTF1 in stone formation, cannot be carried out in humans. The aim of this investigation therefore was to determine whether prothrombin gene expression is present in the rat kidney. Total RNA was isolated from the kidneys and livers of 12 rats. Using reverse transcriptase PCR, mRNAs corresponding to the thrombin and fragment 1 + 2 (F1+2) regions of prothrombin were analysed by agarose gel electrophoresis. The expression of glyceraldehyde 3-phosphate dehydrogenase was also examined to determine whether the quality of the tissue mRNAs was adequate for analyses. The amplified products were identified by sequence analysis. All kidneys displayed evidence of expression of the thrombin and F1+2 domains of the prothrombin gene. Furthermore, the sequences of these PCR-derived products from kidney were identical to those from liver. This suggests that the prothrombins secreted by these two organs are identical. The fact that prothrombin biosynthesis occurs in both the human and rat kidney presents an opportunity for using established rat models of stone disease to evaluate the influence of lithogenic conditions on prothrombin gene expression, and the potential role of UPTF1 in vivo.

Inhibition of calcium oxalate crystal growth and aggregation by prothrombin and its fragments in vitro: relationship between protein structure and inhibitory activity

During blood coagulation, prothrombin (PT) is ultimately degraded to three fragments, thrombin, fragment 1 (F1) and fragment 2 (F2), which, collectively, contain all of the structural features of PT. One of these fragments, F1, is excreted in human urine and is the principal protein occluded into calcium oxalate (CaOx) crystals precipitated from it. This urinary form of F1, which we have named urinary prothrombin fragment 1 is present in calcium stones and is a potent inhibitor of CaOx crystallization in urine in vitro. The aim of this study was to determine whether PT itself and its other activation products, namely, thrombin, F1 and F2 also inhibit CaOx crystallization, by comparing their effects in a seeded, inorganic crystallization system. A secondary objective was to assess the relationship between the structures of the proteins and their inhibitory activities. PT was isolated from a human blood concentrate rich in vitamin K-dependent proteins. Following initial cleavage by thrombin, the resulting fragments, F1 and F2, were purified by a combination of reversed phase HPLC and low pressure column chromatography. The purity of the proteins was confirmed by SDS/PAGE and their individual effects on CaOx crystallization were determined at the same concentration (16.13 nM) in a seeded, metastable solution of CaOx using a Coulter Counter. [14C]Oxalate was used to assess deposition of CaOx and crystals were visualized using scanning electron microscopy. The Coulter Counter data revealed that the proteins reduced the size of precipitated crystals in the order F1 > PT > F2 > thrombin. These findings were confirmed by scanning electron microscopy which showed that the reduction in particle size resulted from a decrease in the degree of crystal aggregation. [14C]Oxalate analysis demonstrated that all proteins inhibited mineral deposition, in the order F1 (44%) > PT (27.4%) > thrombin (10.2%) > F2 (6.5%). It was concluded that the gamma-carboxyglutamic acid domain of PT and F1, which is absent from thrombin and F2, is the region of the molecules which determines their potent inhibitory effects. The superior potency of F1, in comparison with PT, probably results from the molecule's greater charge to mass ratio.

The effect of warfarin therapy on the charge properties of urinary prothrombin fragment 1 and crystallization of calcium oxalate in undiluted human urine

Urinary prothrombin fragment 1 (UPTF1) is the principal protein in calcium oxalate (CaOx) crystals precipitated from human urine and is a potent inhibitor of CaOx crystallization, a property that should depend, at least in part, upon the extent of gamma-carboxylation of the 10 glutamic residues in its N-terminal region. Warfarin therapy limits full gamma-carboxylation of vitamin K-dependent proteins, including UPTF1. The aims of this study were to determine the effect of warfarin therapy on UPTF1, its occlusion into CaOx urinary crystals, and its influence on the crystallization of CaOx in undiluted human urine. In the first part of the study, urines were collected from six men prior to cardiac surgery and after stabilization on long-term warfarin treatment. Proteins in the urines and in the matrix of CaOx crystals precipitated from them were analyzed by two-dimensional SDS-PAGE and Western blotting. In urine, at least two charge variants of UPTF1 with low isoelectric point (pI) values were detected before and during warfarin therapy, but additional higher pI forms of the protein were also seen during anticoagulation. Nonetheless, the majority of UPTF1 was present in the more fully gamma-carboxylated state. CaOx crystals precipitated from the same urine samples contained only low pI forms of UPTF1. The effect of warfarin treatment on CaOx crystallization in urine was tested by collecting two consecutive 24-h urine samples from 16 men prior to cardiac surgery and during subsequent warfarin treatment. CaOx crystallization was induced in each sample by the addition of sodium oxalate. The size and volume of the particles deposited were determined using a Coulter counter, and the crystals were examined by scanning electron microscopy (SEM). There were no significant differences between the urinary metastable limits before or during warfarin treatment or in the total volume of crystals precipitated. A slight increase in the mean diameter of the crystalline particles precipitated from the urines during anticoagulant therapy was not significant. SEM showed little evidence of changes in overall particle size, although individual crystals of CaOx tended to be larger during warfarin treatment. It was concluded from these studies that the binding of UPTF1 to CaOx crystal surfaces is related to the degree of gamma-carboxylation of its Gla domain, which would also influence the protein's inhibitory effects on CaOx crystallization. However, during warfarin therapy the majority of UPTF1 exists in a highly charged state, indicating that it is completely, or almost completely, gamma-carboxylated, which would explain the lack of any difference between CaOx crystallization parameters in the urine of subjects before and during warfarin administration. We conclude that physiologically significant reductions in the inhibitory potency of UPTF1 would be likely to occur only as a result of proscription of gamma-carboxylation more extensive than that induced by warfarin.

Gene expression of prothrombin in the human kidney and its potential relevance to kidney stone disease

OBJECTIVE

To determine whether urinary prothrombin fragment 1 (UPTF1), which shows considerable promise as a critical determinant of calcium oxalate (CaOx) stone formation, is manufactured by the human kidney.

MATERIALS AND METHODS

Ribonucleic acid was isolated from eight kidneys, two spleens and one liver. Using reverse transcriptase-polymerase chain reaction, mRNA corresponding to the UPTF1 portion of prothrombin was analysed by agarose-gel electrophoresis and Southern blotting.

RESULTS

Six kidney specimens showed clear evidence of prothrombin gene expression; expression in the kidney was less than that in the liver.

CONCLUSION

This is the first demonstration of prothrombin gene expression within the human kidney, a finding that not only has implications for CaOx stone disease but also potentially for blood coagulation.

Comparison of plasma prothrombin and factor VII and urine prothrombin F1 concentrations in patients on long-term warfarin therapy and those in the initial phase

Control of warfarin anticoagulation during the initial phase of therapy is difficult and empirically based. Plasma and urine samples were obtained from normal controls, patients under stable anticoagulation, and patients in the initial phase of anticoagulation. Total plasma prothrombin, des-carboxy (non-adsorbable with barium chloride) prothrombin, and native (total minus non-adsorbable) prothrombin were quantitated using Echis carinatus venom activation. Functional plasma factor VII (VII) was measured using a one-stage clotting assay. Total and des-carboxy urine prothrombin F1 (F1) were measured by ELISA. All urine F1 in normals and both anticoagulated groups was adsorbed by barium chloride. Plasma des-carboxy prothrombin concentration was similar for the two anticoagulated groups and did not correlate with 1/INR. Native prothrombin correlated with 1/INR in both the stable (r = 0.76) and initial phase (r = 0.74) groups. For any given INR, the subjects on stable anticoagulation had lower native prothrombin concentrations than the initial phase patients. Functional factor VII concentration also correlated significantly with 1/INR in both the stable (r = 0.64) and initial phase (r = 0.76) patients. Unlike native prothrombin, VII concentrations did not vary between the two cohorts for any given INR. Previous studies indicate that native prothrombin is a superior predictor of both hemorrhagic and thromboembolic complications during warfarin therapy. Our findings indicate that VII, and not prothrombin, may be the predominant factor monitored by the INR. This further supports the need to reevaluate the usefulness of the INR in the monitoring of warfarin therapy during the initial phase.

Further evidence linking urolithiasis and blood coagulation: urinary prothrombin fragment 1 is present in stone matrix

The fact that organic material is always present and distributed throughout each renal calculus suggests that it may play a role in stone formation. The organic matrix of calcium oxalate (CaOx) crystals freshly generated in urine in vitro contains urinary prothrombin fragment 1 (UPTF1) as the principal protein. In this initial study, matrix was extracted from 12 renal calculi and evaluated for the presence of UPTF1 using Western blotting. UPTF1 was present in all eight stones whose principal component was CaOx, and in one of two stones which consisted mainly of calcium phosphate (CaP). UPTF1 was absent from the two struvite calculi examined. The relationship between CaP and UPTF1 was explored further. Matrix harvested from CaP crystals freshly generated in urine in vitro was also shown to contain UPTF1 as its principal component. Our inability to detect UPTF1 in one mixed CaOx/CaP stone may be related to our methods of matrix retrieval, while its absence from two struvite stones argues against it being present in the other stones merely as a consequence of passive inclusion. This absence may be related to the alkaline environment typical of struvite stone growth. The finding that UPTF1 is present in some renal stones provides the first direct evidence that links blood coagulation proteins with urolithiasis.

Blood coagulation proteins and urolithiasis are linked: crystal matrix protein is the F1 activation peptide of human prothrombin

OBJECTIVES

To determine the relationship between prothrombin and crystal matrix protein (CMP). CMP is the predominant protein found in the organic matrix of calcium oxalate (CaOx) crystals generated from human urine and is a 31 kDa glycoprotein, whose N-terminal amino acid sequence shares homology with human prothrombin.

MATERIALS AND METHODS

CaOx crystallization was induced in ultrafiltered (UF) human urine containing either plasma or serum derived from the same healthy donor, by the addition of sodium oxalate. The crystals were demineralized and the resulting protein extracts analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting, using antibodies raised against human prothrombin and the C-terminus of prothrombin fragment 1 + 2 (F1 + 2).

RESULTS

Prothrombin was detected in extracts of crystals precipitated from the UF urine in the presence of plasma, while CMP was completely absent. Crystals precipitated from UF urine supplemented with serum contained relatively large amounts of F1 + 2 and a protein with the same electrophoretic mobility as CMP. Analysis of a standard preparation of F1 + 2 which also contained prothrombin fragment 1 (F1) as a minor contaminant, showed a protein with electrophoretic and staining properties comparable to CMP.

CONCLUSION

CMP is a urinary form of F1, a degradation product of prothrombin possessing the domain rich in gamma-carboxyglutamic acid, which may have undergone some molecular modification either before or after its release into the urine.

Partial factor IX protein in a pedigree with hemophilia B due to a partial gene deletion

A partial gene product was identified in a pedigree with hemophilia B due to a partial deletion of the Factor IX gene (Chen, S.-H.,S. Yoshitake, P.F. Chance, G.L. Bray, A.R. Thompson, C.R. Scott, and K. Kurachi, 1985, J. Clin. Invest., 76:2161-2164). Levels of this mutant protein in plasma of affected family members studied ranged from 24 to 36 ng/ml (0.6-0.9 U/dl or percent of normal) by a solid-phase immunoassay which is sensitive and specific for the calcium-dependent conformation of human Factor IX. No Factor IX antigen could be detected in patients' plasmas by a non-calcium-requiring monoclonal anti-Factor IX antibody (less than 2 ng/ml). The unconcentrated urine from the five affected family members and four obligate heterozygotes the five affected family members and four obligate heterozygotes tested contained calcium-dependent Factor IX antigen levels ranging from 64 to 160 ng/ml (1.6-4.0 U/dl) and from 10 to 68 ng/ml (0.25-1.7 U/dl), respectively. Of nine normal volunteers screened, three had detectable calcium-dependent antigen in unconcentrated first morning-voided urines with 9.6-16.8 ng/ml (0.24-0.42 U/dl), while the remaining six had detectable urinary antigen only after a 10-fold concentration. Abnormal and normal urinary Factor IX antigen species were concentrated, immunoaffinity purified, electrophoresed, immunoblotted, and distinguished by autoradiography after incubation with 125I-polyclonal calcium-requiring anti-Factor IX. After reducing purified or concentrated samples, a single abnormal 36,000-mol-wt band was identified in the urines from the four affected family members and four obligate heterozygotes tested. Electrophoresis of the reduced urinary Factor IX antigen from the one normal subject tested showed a broad 15,000-20,000-mol-wt band. This normal band was smaller than the species in patients' urines, and was seen as a minor component in the samples from the heterozygotes. No abnormal antigen could be detected in urine from the two other female family members tested. Thus, abnormal urinary Factor IX antigen represents a marker for the presence of the hemophilic Factor IX gene in this family.

Interaction of human alpha-thrombin and gamma-thrombin with antithrombin III, protein C and thrombomodulin

Conversion of human alpha-thrombin to gamma-thrombin by limited proteolysis resulted in a decrease in the inactivation rate of the enzyme by antithrombin III. The second-order rate constants were similar but significantly different: 11 +/- 1.7 X 10(3) and 7 +/- 0.5 X 10(3) M-1 s-1 for alpha- and gamma-thrombin respectively. This difference is probably related to a slight change in reactivity of the catalytic site, rather than to a structural alteration of the recognition site for antithrombin III. The rate of protein C activation, measured in the absence of thrombomodulin, was greatly reduced by conversion of alpha-thrombin to gamma-thrombin. In addition, gamma-thrombin failed to displace alpha-thrombin from its complex with thrombomodulin, as demonstrated by measuring either the rate of protein C activation by thrombin-thrombomodulin, or the fibrinogen clotting activity of thrombin-thrombomodulin, in the presence of competing diisopropylphospho-thrombin. It is concluded that the recognition sites involved in protein-C-thrombin and thrombomodulin-thrombin interactions are both dramatically affected by the loss of peptide material occurring during the conversion of alpha-thrombin to gamma-thrombin and/or by the resulting conformational changes.