The action of factor Xa, thrombin and trypsin on human factor II

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.

The occurrence of beta-hydroxyaspartic acid in the vitamin K-dependent blood coagulation zymogens

Previous work has shown that two vitamin K-dependent plasma zymogens, factor X and protein C, each contain one residue of erythro-beta-hydroxyaspartic acid. In the present study, prothrombin, factor VII and factor IX were subjected to amino acid analyses for beta-hydroxyaspartic acid. Factor IX and factor VII each contain one residue of erythro-beta-hydroxyaspartic acid. Edman sequence analyses revealed that this residue occurs at position 64 in human and bovine factor IX. Inasmuch as the nucleotide sequence codes for aspartic acid at this position, it appears highly likely that beta-hydroxyaspartic acid is formed in these proteins by a post-translational hydroxylation of aspartic acid. In contrast, neither human nor bovine prothrombin contain beta-hydroxyaspartic acid.

Surface-governed molecular regulation of blood coagulation

Among extracellular biological processes the spatial control of blood clotting is a unique phenomenon. Localization in space has very important consequences in both normal and pathological conditions. Under physiological circumstances a clot is formed only in the vicinity of injury, albeit the prerequisites of coagulation are almost completely given in the whole circulation. The local character of blood clotting is secured by the following major conditions: The regulatory signal initiating coagulation-the damaged vascular wall-is itself a surface on which the majority of clotting reactions take place. The first enzyme, factor XII, of the intrinsic coagulation pathway is activated on the collagen fibers exposed in the damaged vascular wall, although the significance of this reaction in respect of the clotting process is ambiguous. On the membrane of platelets adhered to the damaged blood vessel is activated factor XI, too, which is a well-established participant of the intrinsic clotting process. The further consecutive reactions of coagulation are confined to the surface produced by injury, because the enzymes involved contain gamma-carboxyl-glutamyl side chains which are anchored through calcium bridges to the phospholipids of the platelet membrane. The last enzyme of the sequence is thrombin, which is released from the surface. The reactions taking place on the surface form an enzyme cascade, which amplifies the relatively weak triggering signal by several orders of magnitudes. Amplification is ensured not only by the enzyme-substrate relationship of the consecutive reaction partners, but also by spatial confinement, which endows the process with higher efficacy than could be expected on a statistical basis from reactions in solution. It contributes to the efficiency of enzyme cascade that the non-enzymatic regulatory proteins increase the activity of factors IXa and Xa, and thereby the overall process. While the partner of factor IXa, factor VIII, is captured from plasma, factor V, the partner of factor Xa, is derived from the platelets adhered to the damaged surface and orients the binding of factor Xa. The surface localization ensures the protection of the members of clotting system: In the activator complexes found on the surface, the spatial arrangement of clotting factors prevents the inactivation of factors by physiological inhibitors or by proteolytic enzymes and specific antibodies that appear in the circulation in pathological conditions. Platelet factor 4, derived from platelets, binds heparin and thereby markedly decreases the reactivity of antithrombin III, the physiological inhibitor of clotting factors. The above two circumstances are

Partially carboxylated prothrombins. II. Effect of gamma-carboxyglutamyl residues on the properties of prothrombin fragment 1

Purified prothrombin fragments 1 derived from normal (10-carboxyglutamyl) and dicoumarol-induced 7-, 5-, 2-, 1-, and 0-carboxyglutamyl prothrombins contained the same number of gamma-carboxyglutamyl residues as their respective parent molecules. The effect of gamma-carboxyglutamyl residues was more pronounced on the fragments 1 than on the prothrombins. Consequently, the pI values of the fragments 1 were very well differentiated, with normal fragment 1 focusing at pH 3.58, 7-carboxyglutamyl fragment 1 at 3.79, 5- at 3.97, and 2- at pH 4.29. Similarly, by agar gel electrophoresis, normal fragment 1 was the most mobile, followed by 7-, 5-, 2-, 1- and lastly 0-carboxyglutamyl fragment 1. Because of Ca2+ being bound to the carboxyglutamyl residues, the electrophoretic mobility of normal fragment 1, in the presence of Ca2+, was reduced the most, followed by 7-, 5- and then 2-carboxyglutamyl fragment 1, while the mobilities of the 1- and 0-carboxyglutamyl fragments 1 were not affected. In contrast to their parent molecules, all of the fragments 1 in the presence of EDTA gave negative immunoprecipitation reactions against antibodies produced against normal prothrombin. In the presence of Ca2+, conversely, the fragments 1 containing comparable amounts of antigenic activity all gave positive reactions. However, the intensity of the immunoprecipitates varied, as normal fragment 1 gave the most prominent immunoprecipitation reaction, consecutively followed by 7-, 5-, 2-, 1- and lastly 0-carboxyglutamyl fragment 1 where the precipitation was so faint that it was hardly visible.

The mechanism of activation of human prothrombin by an activator isolated from Dispholidus typus venom

Purified human prothrombin was activated, both in the absence and in the presence of thrombin inhibitors (diisopropylfluorophosphate or hirudin), by a coagulant principle isolated from Dispholidus typus venom. The process of activation was monitored by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In the absence of thrombin inhibitor, prolonged incubation of prothrombin with the purified venom yielded thrombin, fragment 1 (F 1) and fragment 2 (F 2). In the presence of diisopropylfluorophosphate, which in the experimental conditions used inhibited only partially the thrombin generated activity, products obtained upon activation of prothrombin by venom were F 1 and a two-chain, disulfide-bridged protein of 58 000 daltons called meizothrombin (des F 1). In the presence of hirudin, which fully inhibited thrombin generated activity, prothrombin activation by the venom did not liberate any fragment, but prothrombin was converted to a derivative composed of two disulfide-bridged polypeptide chains of 48 000 and 37 000 daltons, called meizothrombin. These results are similar to those reported by others when studying the process of prothrombin activation by Echis carinatus venom and allow to conclude that Dispholidus typus venom cleaves a bond linking the A and B chains of thrombin, converting prothrombin into meizothrombin. This enzyme is then responsible for the cleavage of the bond linking F 1 and F 2 and the bond linking F2 the A chain of thrombin.

The N-terminal activation fragment of bovine prothrombin. Immunological studies leading to a one step purification

Some immunological studies on prothrombin fragment 1 from bovine prothrombin and its warfarin-induced precursor acarboxyprothrombin are reported. Based on the results, a rapid and simple immunoadsorption method for the isolation of prothrombin fragment 1 in good yield has been established. The method exploits the conformational change induced in the fragment by removal of Ca2+. The principle may be applicable to other gamma-carboxyglutamyl-containing proteins or fragments therof.

The K-test (trypsin clotting time) in coumarin treated patients and in congenital deficiencies and abnormalities of the prothrombin complex

The behavior of K-test (Trypsin clotting time) has been studied in 38 patients on long-term coumarin therapy and in 19 patients with congenital coagulation disorders of the prothrombin complex. All coumarin treated patients showed a clear prolongation of the test. The results obtained were compared with the standard prothrombin time, the Hepato-Quick-test (P-P test) and the Factor II + X test values, observed in the same patients. A good correlation was observed in each instance. The highest correlation was observed between K-test and the Factor II + X test (r=+0,78;t=7,80;p less than 0.001). All congenital coagulation disorders of the prothrombin complex yielded a prolonged K-test value but for Factor VII deficiency. In three patients with this latter condition a perfectly normal value was obtained. The K-test together with the prothrombin time may be useful in the differential diagnosis of factor VII deficiency from factor X deficiency and from the factor X Friuli abnormality.

Factor-V activation by thrombin and its role in prothrombin conversion

Purified coagulation factors and specific antibodies to factor V and factor X were used to investigate the action of thrombin on factor V and the mechanism by which thrombin-treated factor V influences prothrombin activation. The formation of a complex or complexes between phospholipid, factor V, factor Xa and calcium was demonstrated by column chromatography on Sephadex gel, and by immunological analysis of the column fractions including the use of solid-phase antibodies. Kinetic experiments demonstrated that generation of thrombin from purified prothrombin was accomplished by this complex. Pre-treatment of factor V with trace quantities of thrombin resulted in increased yield and rate of thrombin generation. It was shown that phospholipid became saturated when incubated with increasing concentrations of factor V and that the initial saturating concentration of the latter was reduced by pre-treatment with thrombin. The findings confirm that optimum conversion of prothrombin to thrombin is accomplished by a complex or complexes of phospholipid, factor V, factor Xa and calcium and it is suggested that thrombin plays an autocatalytic role in these reactions.