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PubMed2002

Recombinant human prothrombin kringles have potent anti-angiogenic activities and inhibit Lewis lung carcinoma tumor growth and metastases.

Prothrombin, a protein involved in blood coagulation, is a plasma glycoprotein composed of the Gla domain, two adjacent kringle domains, and a serine protease domain. Kringles are triple-disulfide-loop folding domains, which are found in several other blood proteins. In this study, we showed that recombinant human prothrombin kringle-1, -2. and -1-2 (rk-1, -2, -1-2) all have potent anti-angiogenic activities, which inhibit Lewis lung carcinoma (LLC) tumor growth and metastases. Recombinant human prothrombin kringles were expressed by an E. coli expression system and purified to apparent homogeneity from crude E. coli extracts. Purified rk-1, -2, -1-2 migrated with a molecular mass of 14, 19, and 31 kDa, respectively, on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions. rk-1, -2, -1-2 exhibited potent inhibitory effects on bFGF-stimulated bovine capillary endothelial cell growth with half-maximal concentrations (ED50) of approximately 41, 55, and 156 nM, respectively. All of the recombinant human prothrombin kringles also inhibited angiogenesis in the chorioallantoic membrane (CAM) of chick embryos at a dose of 20 microg. Systemic administration of rk-1, -2, -1-2 at a dose of 0.5 mg/kg/day suppressed the growth of primary LLC and at dose of 0.5 and 1.0 mg/kg/day inhibited LLC metastases in C57BL6/J mice lungs through their anti-angiogenic effects.

Amino Acid Sequence↗
PubMed2003

Factor V Leiden and prothrombin gene G20210A mutations in ocular Behçet disease.

PURPOSE: To investigate genetic prothrombotic factors (factor V Leiden and prothrombin gene G20210A mutations) and their relation with retinal vascular occlusions in ocular Behçet disease. METHODS: Thirty Behçet patients were prospectively recruited into the study. Their mean age was 34.2 +/- 8.3 years. All patients underwent complete ophthalmic examination and fluorescein angiography. Of the 30 patients, 15 (16 eyes) had retinal vascular occlusion. Patients were tested for the presence of factor V Leiden and prothrombin gene G20210A mutations by polymerase chain reaction. The results were compared with the frequencies of factor V Leiden in 285 and prothrombin gene G20210A mutation in 182 healthy members of the Turkish population. RESULTS: The prevalence of factor V Leiden mutation was significantly higher in ocular Behçet patients (12/30, 40%), compared with healthy control subjects (28/285, 9.8%) (p < 0.001). Of the 12 Behçet patients with factor V Leiden mutation, eight had retinal vascular occlusion. The prevalence of factor V Leiden was 53.3% (8/15) of the 15 patients with retinal vascular occlusion and 26.7% (4/15) of the remaining 15 patients without vascular occlusion. Prothrombin gene mutation was detected in none of Behçet patients compared with 2.7% (5/182) of the control group. CONCLUSION: These data suggest that factor V Leiden may be an additional risk factor in ocular Behçet disease, whereas factor II mutations do not seem to be relevant.

Adolescent↗
PubMed1987

Turnover of factor X and of prothrombin in rabbits fed on a standard or cholesterol-supplemented diet.

The turnover of prothrombin and of factor X was investigated in rabbits fed on a 1%-cholesterol-supplemented or a standard diet by studying the evolution of radioactivity in blood and in plasma from these animals after the intravenous injection of either 125I-rabbit factor X or 125I-bovine prothrombin. For factor X, half-lives and fractional pool sizes were similar for the two groups of rabbits in the extravascular, intravascular and plasma compartments. However, the equivalent plasma fractional pool size for the two groups of rabbits was only 73% of that in the intravascular compartment. The fractional catabolic rate for the hypercholesterolaemic rabbits [0.064 +/- 0.007 (of the intravascular pool)/h] was not significantly different from that in the rabbits fed on the standard diet (0.074 +/- 0.008/h). However, the absolute catabolic rate, and therefore the rate of synthesis, was significantly higher (1.261 +/- 0.141 mg/day per kg body wt. of rabbit) in the rabbits fed on the cholesterol-supplemented than that in the rabbits fed on the standard diet (0.705 +/- 0.019 mg/day per kg). The prothrombin half-lives and fractional pool sizes were similar for the two groups of rabbits in the extravascular and the intravascular compartments. The fractional catabolic rate for the hypercholesterolaemic rabbits [0.041 +/- 0.003 (of the plasma pool)/h] was not significantly different from that in the rabbits fed on the standard diet (0.035 +/- 0.003/h). However, the absolute catabolic rate and therefore the rate of prothrombin synthesis was significantly higher (3.96 +/- 0.48 mg/day per kg body wt.) in the rabbits fed on the cholesterol-supplemented than that in the rabbits fed on the standard diet (2.24 +/- 0.12 mg/day per kg).

Animals↗
PubMed1997

Prothrombinase is protected from inactivation by tissue factor pathway inhibitor: competition between prothrombin and inhibitor.

The inhibition of prothrombinase by tissue factor pathway inhibitor (TFPI) has been studied in the presence and absence of prothrombin. The rate constant of association of prothrombinase with full-length TFPI was 2.1x10(7) M-1.s-1 and 0.05x10(7) M-1.s-1 for the reaction with C-terminus truncated TFPI (TFPI1-161). The rate constant of dissociation was 0.65x10(-4) s-1 in both cases. The rate constant of inhibition of prothrombinase by TFPI1-161 was similar to that of solution-phase factor Xa. In contrast, phospholipids and factor Va enhanced the association rate of the reaction between factor Xa and full-length TFPI by approx. 20-fold. Although TFPI, and in particular the full-length variant of the molecule, is a potent inhibitor of prothrombinase (overall inhibition constant of 3 pM), we also found that prothrombin competed very effectively with TFPI for the active site of factor Xa in the prothrombinase complex. A 50% reduction of the rate constant of inhibition was measured in the presence of 4 nM prothrombin, i.e. 0.2% of the plasma concentration of prothrombin. The physiological significance of TFPI as an inhibitor of prothrombinase activity is thus questionable.

Animals↗
PubMed1998

Antibodies to prothrombin in antiphospholipid syndrome and inflammatory disorders.

Antiphospholipid antibodies associated with the antiphospholipid syndrome (APS) have been shown to bind plasma proteins, particularly beta 2-glycoprotein I (beta2-GPI). In this study the incidence of antibodies to solid-phase prothrombin was examined in patients with antiphospholipid syndrome and a variety of other inflammatory disorders. Significantly elevated levels of IgG anti-prothrombin (anti-PT) antibodies were detected in 63% of patients with APS (n = 27, median 22 arbitrary units: AU), 33% with SLE (n = 92, median 14 AU). 45% with rheumatoid factor (n = 22, median 16 AU), 21% with carotid artery stenosis (n = 21, median 15 AU), 32% with stroke (n = 38, median 13 AU). 67% of patients with a false positive serology for syphilis (n = 21, median 24 AU), 37% with HIV (n = 30, median 14 AU), 29% with syphilis (n = 14, median 19 AU) and 3% with infectious mononucleosis (n= 30, median 9 AU). In addition, a group of lupus anticoagulant (LA) positive patients (n = 48) was examined for antibodies to prothrombin, beta2-GPI and cardiolipin. 10 (21%) patients had raised levels of IgG anti-PT antibodies, 30 (62%) had significantly elevated levels of anti-beta2-GPI antibodies and 15 (31%) had elevated levels of anticardiolipin antibodies (ACA). Of the LA-positive patients, 15 (43%) were identified with definite APS, eight (23%) with probable APS, two (6%) with possible APS and 10 (28%) patients had no clinical evidence of APS. In conclusion, antibodies to prothrombin were found in a variety of inflammatory disorders and were therefore not specific for the APS. However, identification of the plasma proteins recognized by antibodies from patients with APS may provide insight into the pathogenic mechanisms involved in the heterogenous clinical manifestations of the APS.

Antibodies, Anticardiolipin↗
PubMed1999

Prevalence of mild hyperhomocysteinaemia and association with thrombophilic genotypes (factor V Leiden and prothrombin G20210A) in Italian patients with venous thromboembolic disease.

Mild hyperhomocysteinaemia is an established risk factor for deep vein thrombosis (DVT); few data concerning its potential interaction with thrombophilic genotypes are available at the present time. We investigated 121 thrombosis-free individuals and 111 patients with at least one objectively confirmed episode of DVT. A thrombophilic condition (deficiency in antithrombin, protein C and S, factor V Leiden, prothrombin G20210A) was detected in 25.2% of the patients; mutant factor V or prothrombin genotypes were present in 6.6% of the controls. Hyperhomocysteinaemia was found in 14.4% of patients and 3. 3% of the controls, with a 3.7-fold increase in risk for DVT (95% CI 1.1-12.3). Adoption of different cut-off levels for definition of hyperhomocysteinaemia did not substantially change the magnitude of the risk. Carriership of both hyperhomocysteinaemia and factor V Leiden or prothrombin G20210A was detected in 2.7% of patients for each combination and in none of the controls. An approximate estimate of 30-fold increased risk in carriers of both hyperhomocysteinaemia and factor V Leiden and 50-fold increased risk in carriers of both hyperhomocysteinaemia and prothrombin G20210A was calculated, suggesting a synergistic interaction between hyperhomocysteinaemia and such thrombophilic genotypes. Yet statistical analysis is highly unstable due to the small number of individuals with combined defects. Further investigations on large series of patients are needed.

Adolescent↗
PubMed2000

Prevalence of factor V Leiden and prothrombin G20210A mutations in unselected patients with venous thromboembolism.

We determined the prevalence of factor V Leiden and of prothrombin G20210A mutations in a cohort of unselected outpatients (n = 748) referred for suspected deep vein thrombosis (DVT) and/or pulmonary embolism (PE) and a pooled analysis of similar studies was also performed. Based on the clinical presentation, the prevalence of factor V Leiden was 15.7% in the 83 patients with DVT and 14.1% in the 99 patients with PE compared with 5.3% in patients without DVT and/or PE (control group). The prevalence of the prothrombin G20210A mutation did not differ among the three groups (3.9% for controls, 4. 8% for DVT and 3.9% for PE patients). We then divided the 99 patients with PE by separately analysing those with PE but without DVT (n = 57) and those with PE and DVT (n = 42). Compared with the control group, the prevalence of factor V Leiden was 10.5%, odds ratio (OR) 2.10 [95% confidence interval (95% CI) 0.68-5.45] in patients with primary PE and 19.1%, OR 4.20 (95% CI 1.54-10.30) in patients with DVT and PE. For the prothrombin G20210A mutation, no statistically significant differences were found between the control group and the three other groups. In conclusion, our data and the pooled analysis indicate that patients with primary PE are less often affected by the factor V Leiden mutation. No statistically significant differences were observed between patients and controls for the prothrombin G20210A mutation.

Adult↗
PubMed1998

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.

Biomarkers↗
PubMed2000

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.

Adult↗
PubMed2004

Prothrombin overexpressed in post-natal neurones requires blood factors for activation in the mouse brain.

Thrombin is thought to mediate, through protease-activated receptors, both protective as well as cytotoxic effects. As thrombin receptors are expressed in the CNS, an important question arises as to whether the intact nervous system is able to generate thrombin by activation of its precursor prothrombin, derived endogenously or only upon extravasation following brain injury. To address this question, transgenic mice that express C-terminally haemagglutinin tagged human prothrombin in post-mitotic neurones were generated. In situ hybridization and immunohistochemical analysis showed abundant and widespread cerebral expression of the transgene. Amidolytic assays of brain homogenates and hippocampal slice cultures demonstrated that activation of transgenic prothrombin required added factors, such as snake venom or blood components. This strongly suggests that any possible action of thrombin in the adult CNS depends on blood-derived factors that activate prothrombin. Furthermore, the results are consistent with the idea that in the non-pathological situation an as yet unidentified ligand activates thrombin receptors in the nervous system.

Age Factors↗
PubMed2001

Increased rate of renal transplant failure in patients with the G20210A mutation of the prothrombin gene.

In patients with thrombophilia caused by reduced physiological anticoagulation, renal transplant failure occurs more frequently. Previous studies showed the importance of the protein C system, a physiological anticoagulatory pathway that inhibits thrombus formation. However, excess activation of the hemostatic system also may result in thrombosis. The G20210A mutation in the prothrombin gene is such a prothrombotic risk factor that results in increased thrombus formation because of elevated factor II levels in plasma. We analyzed graft function in 270 consecutive patients who received 311 renal transplants. The presence of a normal or mutated prothrombin allele was determined by polymerase chain reaction amplification and restriction fragment length polymorphism analysis of genomic DNA. Demographic data were extracted from hospital records. Graft survival was calculated for patients with and without the G20210A mutation. We identified 9 patients heterozygous for the G20210A mutation in the prothrombin gene who had received a total of 12 renal transplants. Of these 12 transplants, 2 grafts were lost within the first year. Median graft survival for patients heterozygous for the 20210A allele was 65.9 months (range, 0 to 101 months) compared with 149 months (range, 0 to 237 months) for patients homozygous for the normal 20210 G allele (P = 0.02). The G20210A mutation represented a 2.95-fold (95% confidence interval, 1.03 to 8.46) increase in risk for graft loss. Only 1 patient with this mutation achieved graft function exceeding 101 months. The G20210A mutation of the prothrombin gene is an independent risk factor for graft failure.

Adult↗
PubMed2002

Increased prevalence of the G20210A prothrombin gene variant in acute coronary syndromes without metabolic or acquired risk factors or with limited extent of disease.

AIMS: To investigate the prevalence of the G20210A prothrombin and G1691A factor V gene variants in patients with acute coronary syndrome stratified according to risk factor profile and to extent of coronary disease, in comparison with matched healthy controls. METHODS AND RESULTS: The 20210 prothrombin and the 1691 factor V loci were genotyped in 247 patients < or =65 years of age (190 myocardial infarction and 57 unstable angina as first presentation of disease) and in 247 healthy age- and sex-matched controls. The prevalence of the 1691A factor V allele was similar in cases and controls. The frequency of heterozygotes for the 20210A prothrombin allele was 6.5% among patients and 2.8% among controls (OR 2.4, 95% CI 1.0-5.9), increasing to 8.7% in patients with a family history of myocardial infarction (OR 3.3, 95% CI 1.2-9.1), to 9.9% in patients (n=81) with < or =1 vessel disease (OR 3.8, 95% CI 1.3-10.8), and to 13.0% in patients who were normocholesterolaemic, non-diabetic, normotensive and non-smokers (OR 5.1, 95% CI 1.2-21.4). CONCLUSIONS: These findings suggest that the 20210A prothrombin allele represents an inherited risk factor for acute coronary syndrome among patients who have limited extent of coronary disease at angiography or who lack major metabolic and acquired risk factors.

Acute Disease↗
PubMed2002

Prothrombin levels in newborn infants by the carinactivase-1 method.

A recently developed method to quantitate prothrombin in plasma uses the carinactivase-1 (CA-1) method. The present study was designed to establish the reference value by the CA-1 method in the neonatal period and to explore the effect of gestational age, birth weight, concurrent diseases, and vitamin K administration on the prothrombin levels. We enrolled 78 consecutive neonates. The gestational ages ranged from 28 to 41 weeks, and the birth weight ranged from 850 to 3750 g. Twenty-nine infants had concurrent diseases, and the others (n = 49) were healthy. A 300 microL blood sample was drawn into a plastic syringe containing 60 U freeze-dried buffered heparin. Prothrombin levels did not differ between appropriate-for-date (AFD) and light-for-date (LFD) babies (p = 0.090) or between groups with and without concurrent diseases (p = 0.210). In healthy AFD babies, prothrombin levels correlated with gestational age (r = 0.465, p = 0.003) and birth weight (r = 0.458, p = 0.003). In healthy low-birth-weight infants (n = 14) and those with concurrent diseases (n = 17), the changes after vitamin K administration were not significant. The CA-1 method is of clinical use in monitoring coagulation during the early neonatal period.

Birth Weight↗
PubMed2004

[Dynamics of thrombin-antithrombin-III complex (TAT-III) and prothrombin fragments F1 + 2 during labour with and without aprotinin administration].

OBJECTIVE: The aim of this study was to determine if aprotinin could affect postpartal fibrinolysis when given at the latest 15 min before delivery and if there is a difference between normal delivery and caesarean section. Furthermore we wanted to examine if the thrombin-antithrombin-III-complex (TAT-III) and prothrombin fragments F1 + 2 changed in the peripartal period and if prethrombotic stages could be recognized. PATIENTS AND METHODS: 84 patients (15 - 44 years of age) have been examined (41 normal deliveries, 43 cesarean sections). After giving informed consent and randomization, 30 of these patients were administered 1 Mio KIE aprotinin (Trasylol(R)) at the latest 15 min before delivery (15 normal deliveries, 15 cesarean sections). The results of TAT-III, prothrombin fragments F1 + 2, factor VIII and partial thromboplastin-time (PTT) were collected shortly before and after delivery and 30 and 120 min after detachment of the placenta. RESULTS: Normal deliveries without aprotinin showed a significant increase of TAT-III and an evident increase of prothrombin fragments F1 + 2. After administration of aprotinin this increase was significantly lower. The increase of TAT-III and prothrombin fragments F1 + 2 in patients with caesarean sections was evidently lower than in normal deliveries and was not influenced significantly by aprotinin. Factor VIII and partial thromboplastin time (PTT) showed no relevant changes in all study groups. DISCUSSION AND CONCLUSION: The consumption of coagulation and fibrinolysis factors induced by delivery of the child and detachment of the placenta can be reduced after administration of aprotinin given at the latest 10 - 18 min before partus. This could be used in therapy and prophylactic treatment in high-risk patients (e. g., pre-eclampsia, HELLP syndrome, etc.).

Adolescent↗
PubMed1999

Prothrombin G20210A gene mutation, heparin cofactor II defects, primary (essential) thrombocythemia, and thrombohemorrhagic manifestations.

This article addresses the issue of thromboembolic disorders associated with the prothrombin G20210A gene mutation, with heparin cofactor II (HC-II) defects and with primary (essential) thrombocythemia. The prothrombin gene mutation is of recent discovery, is inherited as an autosomal dominant disorder, and seems to be highly prevalent in the general white population. The incidence is almost as high as that known for factor V Leiden. Both venous and arterial thromboses are noted, especially deep venous thrombosis, including cerebral venous events and myocardial infarction. As with other congenital thrombophilic states, additional risk factors or multiple defects seem to precipitate the events. Although initially elevated plasma prothrombin levels were described in these patients, this is no longer valid for all patients. At this time there is no easy screening test to detect this defect, but, because of the high prevalence, prothrombin G20210A gene mutation should routinely be assayed for in thrombophilic patients. The association between HC-II defects and thromboembolism is more controversial, and reports both confirming and denying this association have been described. The congenital form of HC-II defect is autosomal dominant. HC-II can be determined by its activity and immunologically. HC-II defects very likely play a role in conjunction with other congenital or acquired defects. Acquired HC-II defects are found in association with systemic disseminated intravascular coagulation (DIC) but not with local activation of the hemostasis system. HC-II levels are also decreased in preeclamptic women, and newborns have physiologically low levels. HC-II defects in thrombophilic patients should be considered after the more common disorders have been ruled out. Primary (essential) thrombocythemia can be associated with both thromboembolic events and bleeding. Typical thrombotic manifestations are erythromelalgia and microvascular thrombosis. Also, pregnant females suffer high rates of complications, such as spontaneous abortion. A number of treatment modalities are at present available to not only decrease platelet counts but also manage thromboembolic events.

Family Health↗
PubMed1999

The risk of recurrent deep venous thrombosis among heterozygous carriers of both factor V Leiden and the G20210A prothrombin mutation.

BACKGROUND: Point mutations in the factor V gene (factor V Leiden) and the prothrombin gene (the substitution of A for G at position 20210) are the most common causes of inherited thrombophilia. Whether or not factor V Leiden increases the risk of recurrent deep venous thrombosis is controversial, and there is no information on the risk of recurrence among carriers of both mutations. METHODS: We studied a retrospective cohort of 624 patients who were referred for a first episode of deep venous thrombosis. After excluding 212 patients with other inherited or acquired causes of thrombophilia, we compared 112 patients who were heterozygous carriers of factor V Leiden with 17 patients who were heterozygous for both factor V Leiden and the prothrombin mutation and 283 patients who had neither mutation. The relative risk of recurrent deep venous thrombosis was calculated with use of a proportional-hazards model. RESULTS: Patients who were heterozygous for factor V Leiden alone had a risk of recurrent deep venous thrombosis that was similar to that among patients who had neither mutation (relative risk, 1.1; 95 percent confidence interval, 0.7 to 1.6; P=0.76). In contrast, patients who were heterozygous for both factor V Leiden and the prothrombin mutation had a higher risk of recurrent thrombosis than did carriers of factor V Leiden alone (relative risk, 2.6; 95 percent confidence interval, 1.3 to 5.1; P=0.002). When the analysis was restricted to patients with spontaneous recurrences (i.e., ones that occurred in the absence of transient risk factors for venous thrombosis), the risk among carriers of both mutations, as compared with carriers of factor V Leiden alone, remained high (relative risk, 3.7; 95 percent confidence interval, 1.7 to 7.7; P<0.001), particularly if the first event had also been spontaneous (relative risk, 5.4; 95 percent confidence interval, 2.0 to 14.1; P<0.001). In contrast, the risk of recurrence in the presence of transient risk factors was similar among carriers of both mutations and carriers of factor V Leiden alone. CONCLUSIONS: The risk of recurrent deep venous thrombosis is similar among carriers of factor V Leiden and patients without this mutation. Carriers of both factor V Leiden and the G20210A prothrombin mutation have an increased risk of recurrent deep venous thrombosis after a first episode and are candidates for lifelong anticoagulation.

Adolescent↗
PubMed1973

The mode of action of vitamin K. Isolation of a peptide containing the vitamin K-dependent portion of prothrombin.

Previous evidence has indicated that vitamin K functions in a metabolic step that specifically alters a precursor protein and converts it to biologically active prothrombin. This alteration appears to be related to the biosynthesis or attachment of a noncarbohydrate prosthetic group [Nelsestuen and Suttie (1972) J. Biol. Chem. 247, 8176]. We report the isolation of a peptide from bovine prothrombin that contains the vitamin K-dependent region of the molecule. The properties of the isolated peptide would appear to account for the major differences observed between prothrombin and its biologically inactive form produced by animals administered Dicumarol orally. These differences are quantitative absorption onto insoluble barium salts and the ability to bind calcium ions. The observed properties of this peptide provide direct evidence for the presence of a covalently bound noncarbohydrate prosthetic group(s) on the prothrombin molecule.

Amino Acids↗
PubMed1974

A comparison of bovine prothrombin, factor IX (Christmas factor), and factor X (Stuart factor).

A comparison has been made of the electrophoretic behavior, chemical composition, amino-terminal sequence, and immunological properties of bovine prothrombin, factor IX (Christmas factor), and factor X (Stuart factor). Some immunological crossreactivity was found between the antibody to prothrombin and factor X although prothrombin and factor X differ substantially in amino-acid and carbohydrate composition. Considerable amino-acid sequence homology was found in the amino-terminal portion of prothrombin, factor IX, and the light chain of factor X. These data provide further evidence to support the hypothesis that at least three of the vitamin K-dependent clotting factors have evolved from a common ancestral gene.

Amino Acid Sequence↗