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PubMed1999

Lupus anticoagulants form immune complexes with prothrombin and phospholipid that can augment thrombin production in flow.

Lupus anticoagulants (LA) are a family of autoantibodies that are associated with in vitro anticoagulant activity but a strong predisposition to in vivo thrombosis. They are directed against plasma phospholipid binding proteins, including prothrombin. We found that a murine monoclonal antiprothrombin antibody and 7 of 7 LA IgGs tested enhanced binding of prothrombin to 25:75 phosphatidyl serine:phosphatidyl choline vesicles in a concentration-dependent manner. We hypothesized that enhanced binding of prothrombin to phospholipid in the presence of LA IgG might result in increased thrombin production when reactions are performed in flow. Thrombin production by purified prothrombinase components was measured in a phospholipid-coated flow reactor. The flow reactor was incubated with prothrombin, calcium ions, and the IgGs and then perfused with prothrombin, calcium ions, the IgGs, factor Va, and factor Xa. A murine monoclonal antiprothrombin antibody and 4 of 6 LA IgGs from patients with a history of thrombosis increased thrombin production up to 100% over control in the first 15 minutes. In summary, LA IgGs concentrate prothrombin on a phospholipid surface that can augment thrombin production by prothrombinase in flow. These observations suggest that LA might propagate coagulation in flowing blood by facilitating prothrombin interaction with the damaged blood vessel wall.

Animals↗
PubMed2002

No association of plasma prothrombin concentration or the G20210A mutation with incident cardiovascular disease: results from the Cardiovascular Health Study.

Prothrombin is a key factor in blood clotting, a process intimately involved in thrombotic disease. We assessed prothrombin levels and G20210A genotype in a case-control study within the Cardiovascular Health Study. Cases included angina, myocardial infarction, stroke, and the presence of MRI-detectable infarcts (n approximately 250 each). Population-based controls free of clinical cardiovascular disease (CVD) (n approximately 500) and a subset free of clinical and subclinical CVD (n approximately 250) were used for comparison. The 20210 A allele, frequency 2.9%, was associated with higher mean prothrombin levels: 166.3 vs. 139.5 microg/ml (P <0.001). Significant correlates of prothrombin included gender, plasma lipids, other vitamin K-dependent proteins, and inflammatory markers, but not race, smoking, hypertension, diabetes, measures of subclinical CVD, or markers of procoagulant activity. Compared to controls, neither genotype nor prothrombin level was associated with any CVD case group. We conclude that, in the elderly, neither prothrombin level nor 20210 genotype were associated with either CVD risk factors or events. This is consistent with the lack of association of prothrombin levels with measures of underlying CVD or procoagulant markers.

3' Untranslated Regions↗
PubMed2002

Prothrombin G20210A is a bifunctional gene polymorphism.

The G20210A polymorphism has been shown to alter the efficiency of prothrombin mRNA processing. Here we show that the G20210A mutation also alters prothrombin mRNA stability. Three-fold more prothrombin protein and mRNA were produced in NIH-3T3 cells transfected with the prothrombin cDNAs containing the 20210A variant compared to cells expressing the 20210G variant. mRNA stability assays using chimeric globin transcripts harboring the G or A variant of the 97 nt prothrombin 3'-UTR indicated that the 20210G variant conferred greater instability to the globin reporter transcript than the A variant in transfected HepG2 cells. Both variants of the prothrombin 3'-UTR were shown to provide binding sites for a number of cellular proteins including HuR, an RNA binding protein associated with mRNA stability. Our results indicate that the G20210A is a bifunctional polymorphism, as it not only alters the efficiency of mRNA processing, but also the decay rate of prothrombin mRNA.

3' Untranslated Regions↗
PubMed1991

Proteolytic formation of either of the two prothrombin activation intermediates results in formation of a hirugen-binding site.

Hirugen, a synthetic dodecapeptide corresponding to the carboxyl-terminal amino acids 53-64 of hirudin, binds within a deep groove in thrombin that contains a cationic region referred to as the anion-binding exosite. This region is important in many of the binary interactions of thrombin with macromolecular substrates and cofactors. Fluorescein-labeled hirugen was used to probe which steps in the prothrombin activation process generate this anion-binding exosite. Two activation cleavage sites exist in bovine prothrombin. Cleavage at Arg274-Thr275 releases the activation fragments to generate the thrombin precursor, prethrombin 2. Cleavage of prothrombin within a disulfide loop at Arg323-Ile324 leads to formation of meizothrombin with no loss of peptide material but with formation of amidolytic activity. Cleavage of the same bond in prethrombin 2 generates thrombin. Hirugen, labeled at the amino terminus with fluorescein isothiocyanate, does not bind to prothrombin but does bind to thrombin (Kd = 9.6 +/- 1.2 x 10(-8) M), prethrombin 2 (Kd = 1.3 +/- 0.1 x 10(-7) M), thrombin-fragment-2 complex (Kd = 1.1 +/- 0.2 x 10(-6) M), and meizothrombin (Kd = 1.6 +/- 0.5 x 10(-8) M). Prothrombin fragment-2 and hirugen both bind independently to thrombin. A ternary complex can form with hirugen and fragment-2 and either thrombin or prethrombin 2, suggesting that fragment-2 and hirugen bind to discrete sites. Hirugen also alters the active site conformation of thrombin as detected by modulation of synthetic substrate hydrolytic activity. These studies suggest that conformational changes, rather than alleviating steric hindrance, are responsible for the formation of the hirugen-binding site during prothrombin activation. Furthermore, this conformational change can be effected by the cleavage of either of the two bonds required for activation of prothrombin.

Amino Acid Sequence↗
PubMed1991

Formation of meizothrombin as intermediate in factor Xa-catalyzed prothrombin activation on endothelial cells. The influence of thrombin on the reaction mechanism.

Incubation of prothrombin on cultured human umbilical vein endothelial cells with factor Xa and calcium ions induced the activation of prothrombin. The mechanism of prothrombin activation was analyzed on sodium dodecyl sulfate gels using immuno- and amido-blotting techniques. It was demonstrated that meizothrombin was formed as an intermediate in prothrombin activation on the endothelial cell surface. In addition, considerable amounts of meizothrombin des-fragment-1 accumulated during prothrombin activation and were not further converted to thrombin. Although preincubation of the endothelial cells with thrombin did not influence the formation of meizothrombin, addition of hirudin to the prothrombin activation mixture inhibited the formation of meizothrombin and meizothrombin des-fragment-1 almost completely. This indicated that the activity of endogenously formed thrombin influenced the formation of meizothrombin via a feedback mechanism. The increased formation of meizothrombin and accumulation of meizothrombin des-fragment-1 in a latter phase of prothrombin activation points to a regulatory mechanism in hemostasis which subdues the formation of the procoagulant alpha-thrombin.

Calcium↗
PubMed1987

Study on a new chromogenic substrate for the prothrombin time determination.

The aim of our study was to evaluate the possibility of using a chromogenic substrate for the prothrombin time determination. The reagent used by us (Chromoquick) is composed of a human placenta thromboplastin and chromogenic substrate (Tos-Gly-Pro-Arg-5-amino-2-nitrobenzoic acid-isopropylamide), calcium chloride and a buffer. Normal subjects, patients with liver disease, patients on oral anticoagulant therapy, patients on heparin therapy, heterozygous and homozygous patients for prothrombin complex defects and other miscellaneous conditions have been investigated. The results of chromoquick have been related with standard prothrombin time obtained using a human placenta thromboplastin (Thromborel) and rabbit brain and lung thromboplastin (Simplastin). The normal range was 18-23 s for chromoquick and 13.5-15.5 s for the standard prothrombin times using Thromborel and Simplastin. In all groups of patients examined we noticed a significant correlation between the chromogenic and the classic prothrombin times with r values varying between +0.505 and +0.947. The statistical significance resulted from p values varying between less than 0.05 and less than 0.001. Only in the case of some heterozygotes for prothrombin complex factor defects the values obtained have not been unequivocal in the sense that in a few instances the heterozygotes seemed to escape detection. Therefore, it seems that the introduction of chromogenic substrates in laboratory practice for the prothrombin time determination is possible and can offer considerable advantages like standardization and automation. The only disadvantage may be caused by costs involved.

Acenocoumarol↗
PubMed1988

Phospholipid binding properties of bovine prothrombin peptide residues 1-45.

The present study investigates the unique contribution of the NH2-terminal 33 residues of prothrombin, the gamma-carboxyglutamic acid (Gla) domain, to the Ca(II) and phospholipid-binding properties of prothrombin. Two Gla domain peptides, 1-42 and 1-45, produced by chymotryptic cleavage of prothrombin fragment 1 (residues 1-156 of the amino terminus of bovine prothrombin) and isolated by anion-exchange chromatography were utilized to characterize the Gla domain of prothrombin. This investigation utilized several experimental approaches to examine the properties of the Gla domain peptides. These studies were somewhat hampered by the metal ion-induced insolubility of the peptides. However, the 1-45 peptide was specifically radioiodinated, which facilitated the study of this peptide at low concentrations. In contrast to prothrombin fragment 1, the intrinsic fluorescence of both 1-42 and 1-45 was not quenched upon the addition of 1 mM Ca(II) or any concentration of Mg(II). Equilibrium dialysis studies revealed that the 1-42 peptide bound three Ca(II) ions noncooperatively, whereas fragment 1 binds seven Ca(II) ions in a positive cooperative manner. Ca(II)-promoted conformational changes are observed by comparison of electrophoretic mobility changes in the presence of increasing Ca(II) concentrations. Prothrombin, fragment 1, and the Gla domain peptides 1-42 and 1-45 exhibited similar electrophoretic mobility behavior in the presence of Ca(II) ions. The radiolabeled 1-45 peptide was found to comigrate with phospholipid vesicles on gel permeation chromatography in the presence of Ca(II). Fragment 1 was shown to inhibit this Ca(II)-dependent phospholipid binding of 1-45, demonstrating that the 1-45 peptide does possess the necessary phospholipid-binding structure. Furthermore, a metal ion-dependent conformational monoclonal antibody, F9.29, was inhibited from binding fragment 1 by the 1-42 peptide.

Amino Acid Sequence↗
PubMed1988

A comparison of seven prothrombin time reagents--development of an evaluation strategy.

The control of p.o. anticoagulant therapy by the use of prothrombin times or ratios is one of the major functions of a clinical coagulation laboratory. European prothrombin reagents tend to be more sensitive to the effects of p.o. anticoagulants than traditional North American rabbit brain thromboplastin reagents. The clinical importance of this in vitro observation has been emphasized by the results of two recent clinical trials which both suggested that the less intense anticoagulation therapy that results from the use of a European-type prothrombin reagent may be safer. To minimize the clinical effects of differences in prothrombin time reagent formulation, a global correction factor has been developed--the international normalized ratio (INR). Despite this advance in international standardization, individual laboratories need a rapid and efficient method to help select the most appropriate prothrombin reagent for the clinical management of their local patient population. This study has examined the response of a variety of commercially available prothrombin time reagents to normal plasmas and those from anticoagulated patients. Using both classical sampling theory and multiple range testing, it was demonstrated that as few as 20 estimations on normal plasmas and 50 on anticoagulated specimens will permit a clinical laboratory to select a suitable prothrombin time reagent for anticoagulant control of their specific local patient population.

Anticoagulants↗
PubMed1988

Metal ion blockage of tritium incorporation into gamma-carboxyglutamic acid of prothrombin. Stoichiometry of gamma-carboxyglutamic acid to Gd3+ for the high affinity sites.

Prothrombin possesses two high affinity and four low affinity gamma-carboxyglutamic acid (Gla)-dependent gadolinium binding sites. Earlier work (Price, P. A., Williamson, M. K., and Epstein, D. J. (1981) J. Biol. Chem. 256, 1172-1176) has shown that tritium can be specifically incorporated at the gamma-carbon of Gla in proteins at pH 5. In the present work we show that inclusion of saturating concentrations of Ca2+ in nondenaturing buffer systems ranging from pH 5.5 to 8.5 prevents the exchange of tritium into all 10 Gla residues of prothrombin. Similarly, saturating concentrations of Gd3+ prevent tritium incorporation into Gla at pH 5.5. Positive cooperativity was observed for the binding of Gd3+ to human prothrombin (at pH 5.5) for the two high affinity sites (Kd congruent to 35 nM). The four low affinity sites bind Gd3+ with a Kd congruent to 5 microM. Incubation of prothrombin ranging in concentrations from 10 to 40 microM with 2 eq of Gd3+ at pH 5.5 prevents 5.7 (average of seven determinations) Gla residues from tritium incorporation. Sedimentation velocity experiments conducted at pH 5.5 indicate that prothrombin in the presence of saturating concentrations of Gd3+ polymerizes, most likely, to a trimer. Further, in the presence of 2 eq of Gd3+, calculated percent weight average concentration of monomer prothrombin is congruent to 100% at 10 microM, approximately equal to 95% at 20 microM, and congruento to 80% at 40 microM protein concentration. Thus, it appears that under conditions in which prothrombin primarily exists as a monomer, occupancy of the initial two metal binding sites by Gd3+ involves six Gla residues.

1-Carboxyglutamic Acid↗
PubMed1986

Formation of meizothrombin as intermediate in factor Xa-catalyzed prothrombin activation.

The conversion of prothrombin into thrombin by Factor Xa requires the cleavage of two peptide bonds in prothrombin. Dependent on the order of cleavage, prethrombin 2 or meizothrombin occurs as intermediate. Since prethrombin 2 has as yet been the only observed intermediate, prothrombin activation is generally considered to proceed via prethrombin 2. In this paper we present new methods that allow differentiation between meizothrombin and thrombin formed during the initial phase of prothrombin activation. These methods, which make use of the different reactivities of meizothrombin and thrombin toward fibrinogen and antithrombin III plus heparin, enabled us to show the generation of considerable amounts of meizothrombin during Factor Xa-catalyzed prothrombin activation. Both meizothrombin and thrombin incorporated the active site-directed fluorescent chloromethyl ketone 5-dimethylaminonaphthalene-1-sulfonyl-Glu-Gly-Arg-CH2Cl. Gel electrophoretic analysis of chloromethyl ketone-treated aliquots of prothrombin activation mixtures confirmed meizothrombin formation. These observations demonstrate that prothrombin may also be converted into thrombin via meizothrombin.

Animals↗
PubMed1987

Activation of human prothrombin by human prothrombinase. Influence of factor Va on the reaction mechanism.

The kinetics of the activation of human prothrombin catalyzed by human prothrombinase was studied using the fluorescent alpha-thrombin inhibitor dansylarginine-N-(3-ethyl-1,5-pentanediyl)amide (DAPA). Prothrombinase proteolytically activates prothrombin to alpha-thrombin by cleavages at Arg273-Thr274 (bond A) and Arg322-Ile323 (bond B). The differential fluorescence properties of DAPA complexed with the intermediates and products of human prothrombin activation were exploited to study the kinetics of the individual bond cleavages in the zymogen. When the catalyst was composed of prothrombinase (human factor Xa, human factor Va, synthetic phospholipid vesicles, and calcium ion), initial velocity studies of alpha-thrombin formation indicated that the kinetic constants for the cleavage of bonds A or B were similar to the constants that were obtained for the overall reaction (bonds A + B). The progress of the reaction was also monitored by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The results indicated that the activation of human prothrombin catalyzed by prothrombinase proceeded exclusively via the formation of meizothrombin (bond B-cleaved) as an intermediate. Kinetic studies of the cofactor dependence of the rates of cleavage of the individual bonds indicated that, in the absence of the cofactor, cleavage at bond B would constitute the rate-limiting step in prothrombin activation. Progress curves for prothrombin activation catalyzed by prothrombinase and monitored using the fluorophore DAPA were typified by the appearance of a transient maximum, indicating the formation of meizothrombin as an intermediate. When factor Xa alone was the catalyst, progress curves were characterized by an initial burst phase, suggesting the rapid production of prethrombin 2 (bond A-cleaved) followed by its slow conversion to alpha-thrombin. Gel electrophoresis followed by autoradiography was used to confirm these results. Collectively, the results indicate that the activation of human prothrombin via the formation of meizothrombin as an intermediate is a consequence of the association of the cofactor, human factor Va, with the enzyme, human factor Xa, on the phospholipid surface.

Arginine↗
PubMed1985

The role of activated human platelets in prothrombin and factor X activation.

The effect of activated human platelets in intrinsic factor X activation was compared with their effect in prothrombin activation. Compared with unstimulated platelets, platelets triggered by the combined action of collagen plus thrombin showed a tenfold activity increase in prothrombin activation, and a 20-fold rate enhancement in factor X activation. Treatment of collagen plus thrombin-stimulated platelets with N.naja phospholipase A2 almost completely abolished their activity in prothrombin and factor X activation. Since no significant cell lysis occurs during phospholipase treatment, this indicates that platelet phospholipids, exposed at the membrane exterior, play an essential role in the interaction of platelets with the proteins of the prothrombin and factor X-activating complexes. The time course of generation of the procoagulant platelet surface was different when the amount of coagulation factors present in the assay systems was varied. At suboptimal concentrations of coagulation factors, maximum platelet activity was reached after a shorter time period than at saturating concentrations. When measured at suboptimal amounts of coagulation factors, the platelet activity in prothrombin and factor X activation is also more sensitive to phospholipase treatment. Experiments with synthetic phospholipid mixtures show that prothrombin and factor X activation are optimal at low mol% phosphatidylserine when high concentrations of factor Va and factor VIIIa are employed. The optimal mol% phosphatidylserine increases when the concentrations of nonenzymatic protein cofactors are lowered. These findings are discussed in relation to a model in which phosphatidylserine, exposed at the outer surface of activated platelets, plays an essential role in prothrombin and factor X activation. It is proposed that this phosphatidylserine is not homogeneously distributed in the platelet outer membrane, but that areas with different phosphatidylserine density participate in coagulation factor activation.

Blood Coagulation Tests↗
PubMed1978

Prothrombin Quick. A newly identified dysprothrombinemia.

The rarest of reported inherited plasmatic coagulopathies involve prothrombin. Only 10 families with significant reductions of this plasma protein (hypoprothrombinemia) have been observed. Even fewer, six families, have been found to have a functionally abnormal prothrombin (dysprothrombinemia) in their blood. An as yet undefined prothrombin abnormally has been recognized in eight other families. One of the first patients previously identified by Quick and his associates as having a defect in her plasma prothrombin has been shown to have about half the normal amount of prothrombin antigen but virtually no prothrombic function. We propose that this dysprothrombin be designated prothrombin Quick. An additional patient also first described by Quick was found to be truly hypoprothrombinemic--that is, to lack both functional and antigenic prothrombin. Briefly summarized are the other five families with dysprothrombinemia, nine with hypoprothrombinemia, and the eight in whom the defect has not been classified.

Adult↗
PubMed1984

Self-association of bovine prothrombin fragment 1 in the presence of metal ions. Use of a covalent cross-linking reagent to study the reaction.

The interaction of metal ions with prothrombin fragment 1 has been shown by other investigators to result in conformational change(s). Previous studies based on hydrodynamic measurements from other laboratories have suggested that prothrombin fragment 1 will, in addition to undergoing conformational change, self-associate in the presence of metal ions but there is a question regarding the specificity and role of metal ions in this process. The present study has made use of a covalent cross-linking agent, dithiobis(succinimidylpropionate), to study the self-association of prothrombin fragment 1 and has focused on factors influencing the covalent dimerization of bovine prothrombin fragment 1 during reaction with this reagent. Optimal dimerization of bovine prothrombin fragment 1 required the involvement of cations in two separable processes. The "first role" is probably a reflection of a slow conformational change in the bovine prothrombin fragment 1 representing isomerization of a proline-containing peptide bond (Marsh, H. C., Scott, M. E., Hiskey, R. G., and Koehler, K. A. (1979) Biochem. J. 183, 513-517). The "second role" most likely reflects ion bridging with another prothrombin fragment 1 molecule. The ion specificities of these two roles are clearly different. Ions stabilizing the proper conformation (first role) are Ca2+, Sr2+, Mg2+, Mn2+, with Ba2+ having less capability in filling this role. Ions which have activity in the second role (ion bridge formation) are Ca2+, Sr2+, and Ba2+. Mn2+ and Mg2+ cannot fulfill the requirements of this second role and actually inhibit the function of Ca2+.

Animals↗
PubMed1980

The procoagulant effect of platelets on conversion of prothrombin to thrombin in nonanticoagulated plasma.

The effects of normal platelets and dysfunctional platelets on the activities of prothrombin complex components (fluid-phase factor X, factor V, and prothrombin) and on prothrombin conversion products were studied in nonanticoagulated plasma by both functional and physical methods. Rapid centrifugation of small blood volumes at 24 degrees C yielded PRP and PPP before changes could be detected by functional and physical means. It was shown for the first time in native nonanticoagulated PRP that prothrombin and factor V consumption by functional assays depends on physiologically active platelets, since inhibition by PGE and theophylline or by dibutyryl cyclic AMP and acceleration by ADP was observed. These platelet-dependent phenomena occurred in two stages: (1) a decrease in factor V activity coinciding with platelet clumping and (2) a decrease in prothrombin activity simultaneous with clot appearance. Neither of these stages was clearly separated in recalcified citrated plasma. In studies of patients (Glanzmann's thrombasthenia, Hermansky-Pudlak syndrome, and Gray platelet syndrome) inhibition of the first stage and abnormalities in subsequent clotting events occurred only in Gray platelet syndrome patients, whose platelets carry a defect in alpha-granules. Finally, with [3H]prothrombin and SDS-PAGE, prothrombin conversion was found to be platelet-dependent and to proceed mainly through the factor Xa activation pathway.

Adenosine Diphosphate↗
PubMed1977

[Products of bovine prothrombin citraconylation and their activation by factor Xa].

Products of bovine prothrombin acylation by citraconic anhydride, modified to 20--90% have been obtained. Disc-electrophoresis in polyacrylamide gel in the presence of sodium dodecyl sulfate has shown that the citraconylation of prothrombin is accompanied with spontaneous activation, resulting in formation of products with molecular weights identical to those of neoprothrombin C, neoprothrombin T, profragment and fragments A and C. Spontaneous activation upon the citraconylation is never completely recovered: the reaction products always contain a fraction, corresponding in molecular weight to prothrombin. Citraconylation products possess neither coagulating, nor esterase activity. Generation of esterase activity requires the presence of an enzyme--factor Xa, which splits the 323-324 peptide bond (Arg-Ile) in the molecules of prothrombin and intermediate products of its activation. The mechanism of activation of citraconylated prothrombin products by factor Xa does not differ from the mechanism of native prothrombin activation by the enzyme. The esterase activity, which is generated after the incubation with factor Xa, is due to the building of citraconylthrombin and partly of the native thrombin; the latter may be formed at the low degree of prothrombin modification.

Animals↗
PubMed1996

Biosynthesis of prothrombin: intracellular localization of the vitamin K-dependent carboxylase and the sites of gamma-carboxylation.

Prothrombin is a vitamin K-dependent blood coagulation protein that undergoes posttranslational gamma-carboxylation and propeptide cleavage during biosynthesis. The propeptide contains the gamma-carboxylation recognition site that directs gamma-carboxylation. To identify the intracellular sites of carboxylation and propeptide cleavage, we monitored the synthesis of prothrombin in Chinese hamster ovary cells stably transfected with the prothrombin cDNA by immunofluorescent staining. The vitamin K-dependent carboxylase was located in the endoplasmic reticulum and Golgi complex. Antibodies specific to prothrombin processing intermediates were used for immunocytolocalization. Anti-des-gamma-carboxyprothrombin antibodies stained only the endoplasmic reticulum whereas antiproprothrombin antibodies (specific for the propeptide) and antiprothrombin:Mg(II) antibodies (which bind the carboxylated forms of proprothrombin and prothrombin) stained both the endoplasmic reticulum and the Golgi complex. Antiprothrombin:Ca(II)-specific antibodies (which bind only to the carboxylated form of prothrombin lacking the propeptide) stained only the Golgi complex and secretory vesicles, and colocalized with antimannosidase II and anti-p200 in the juxtanuclear Golgi complex. These results indicate that uncarboxylated proprothrombin undergoes complete gamma-carboxylation in the endoplasmic reticulum and that gamma-carboxylation precedes propeptide cleavage during prothrombin biosynthesis.

Acylation↗
PubMed1997

Prothrombin synthesis in the adult and fetal liver.

Plasma levels of blood coagulation zymogens are lower in the newborn than in the adult, with the lowest levels being in preterm infants. It is not known if the lower coagulation factor levels reflect differences in synthesis, secretion or catabolism. Using a rabbit model we have compared prothrombin synthesis in the fetus and adult. In previous studies we attempted to compare transcription in the adult and fetal liver by extraction of mRNA, immobilization on a membrane and hybridization with a labeled cDNA for rabbit prothrombin. Comparison was impaired by the markedly dissimilar composition of fetal and adult rabbit liver; fetal liver is approximately fifty percent hematopoietic tissue even at term (1). In the present study, to obtain a more meaningful comparison we have employed in situ hybridization to compare directly prothrombin expression in adult and fetal liver. We report here that fetal liver contains more prothrombin mRNA than does adult liver. We have further compared prothrombin levels in protein extracts of adult and fetal liver and found that per microgram of extract, fetal liver contains as much prothrombin as does the adult. We conclude that the lower plasma prothrombin levels in the fetus do not reflect a lower rate of synthesis.

Animals↗