Preparation of Highly Purified Prothrombin Complex

Thrombin: An Approach to Developing a Higher-Order Reference Material and Reference Measurement Procedure for Substance Identity, Amount, and Biological Activities

Thrombin, the proteolytic enzyme that catalyzes the transformation of soluble fibrinogen to the polymerized fibrin clot, participates in multiple reactions in blood coagulation in addition to the clotting reaction. Although reference materials have existed for many years, structural characterization and measurement of biological activity have never been sufficient to permit claims of clear metrological traceability for the thrombin preparations. Our current state-of-the-art methods for protein characterization and determination of the catalytic properties of thrombin now make it practical to develop and characterize a metrologically acceptable reference material and reference measurement procedure for thrombin. Specifically, α-thrombin, the biologically produced protease formed during prothrombin activation, is readily available and has been extensively characterized. Dependences of thrombin proteolytic and peptide hydrolytic activities on a variety of substrates, pH, specific ions, and temperature are established, although variability remains for the kinetic parameters that describe thrombin enzymatic action. The roles of specific areas on the surface of the thrombin molecule (exosites) in substrate recognition and catalytic efficiency are described and characterized. It is opportune to develop reference materials of high metrological order and technical feasibility. In this article, we review the properties of α-thrombin important for its preparation and suggest an approach suitable for producing a reference material and a reference measurement procedure that is sensitive to thrombin’s catalytic competency on a variety of substrates.

Acid-induced denaturation and refolding of prothrombin

Structural transitions of the blood coagulation factor prothrombin (extracted from goat blood) in response to reduction of pH were investigated by fluorescence, circular dichroism and light scattering measurements. The study revealed the presence of a partially unfolded state at around pH 3.5, characterized by marked enhancement of fluorescence from ANS bound to the protein, increase of bimolecular rate constant for tryptophan fluorescence quenching and a sharp peak in the light scattering intensity. Further lowering of the pH caused reversal of the trend of variation of these parameters, suggesting that prothrombin folds back to a compact state containing native-like secondary structural elements. The refolded state at low pH (<pH 3) fits the description of the A-state, the end-point of acid-induced denaturation process of several other monomeric proteins, and is a possible candidate for the class of folding intermediates known as molten globules.

Calcium-dependent changes in properties of human prothrombin: a study using high-performance size-exclusion chromatography and gel-permeation chromatography

High-performance size-exclusion chromatography using a TSK 3000 SW column and aqueous gel filtration with Sephacryl S-200 SF have been used to characterize the effects of calcium ions on the hydrodynamic properties of human prothrombin and prethrombin 1. The results suggest that the effective hydrodynamic radius of prothrombin is less in the presence than in the absence of calcium ions. In addition, when using the TSK-3000 SW column, Ca2+-dependent formation of a hydrophobic site in the fragment 1 region of prothrombin results in an apparent further decrease in hydrodynamic radius.

The role of platelet factor V in prothrombin conversion

The contribution of platelet factor V to prothrombin conversion was studied in a purified two-stage system designed to measure the ability of factor V to accelerate prothrombin conversion. When unstimulated gel-filtered platelets (GFP) were substituted for both factor V and phospholipid, thrombin evolution was linear following a long lag time. Gel filtration resulted in considerable phospholipid availability with minimal factor V release. Incubating platelets with collagen in increasing concentrations resulted in marked shortening of the lag time, an increase in the initial rate of thrombin formation, and release of platelet factor V. The inhibition of thrombin formation by preincubation of the platelets with metabolic inhibitors is consistent with previous observations that factor V is released from alpha-granules by collagen in a process requiring metabolic energy. Released platelet factor V added to metabolically inhibited platelets reproduces the acceleration of prothrombin conversion demonstrated in GFP incubated with collagen. Furthermore no acceleration of the clotting time at collagen concentrations used in this study was demonstrated in an assay designed to measure available platelet phospholipid in the presence of excess factor V. The rate of increased thrombin generation produced by collagen stimulation is primarily due to released platelet factor V in the system employed.

Isolation of the high molecular form of bovine factor X and some of its physical properties

A high molecular form of bovine factor X has been isolated from freshly collected bovine blood by BaSO4 absorption, exhaustive washing with 0.001 M BaCl2 and chromatographed on DEAE-cellulose column employing a linear salt gradient. This isolated factor X showed a single protein band on analytical polyacrylamide gel disc electrophoresis. Only one single protein peak was observed in the chromatogram of DEAE-Sephadex A-50 chromatography conducted at 3 degrees C. Sedimentation equilibrium analysis of this bovine factor X revealed no apparent heterogeneity or self association-dissociation phenomena. It yielded a weight-average molecular weight of 74 000 for the native factor X. In the absence of any reducing agent, factor X migrated in dodecyl sulfate gel electrophoresis as a single component with an estimated molecular weight of 74 300. Both dodecyl sulfate gel electrophoresis in the presence of 2-mercaptoethanol and agarose gel chromatography in 6 M guanidinium chloride revealed that this native factor X is composed of two polypeptide chains of molecular weights of 56 000 and 22 100. Factor X can be converted to the enzymatically active factor Xa by Russell's viper venom and in the presence of Ca2+. Factor Xa was purified by DEAE-cellulose chromatography. This Russell's viper venom activated factor Xa also showed a single protein band upon analytical polyacrylamide gel disc electrophoresis. Sedimentation equilibrium analysis of this factor Xa yields a weight-average molecular weight of 59 000 with no apparent heterogeneity or self-association phenomena. In the absence of any reducing agent, factor Xa migrated as a single component in dodecyl sulfate gel electrophoresis with an estimated molecular weight of 58 500. From the results of dodecyl sulfate gel electrophoresis in the presence of 2-mercaptoethanol as well as agarose gel chromatography in 6 M guanidinium chloride, factor Xa is also composed of two polypeptide chains of molecular weights of 36 700 and 22 800. Therefore, the heavy and light chains of both native factor X and factor Xa are linked together by disulfides. Great care was taken in washing the BaSO4 precipitate and it is this effective washing which enabled us to isolate the higher molecular from of bovine factor X.

Sheep prothrombin: purification and partial characterization

A procedure for the preparation of highly purified sheep prothrombin is described. The purified zymogen, when subjected to disc gel electrophoresis in polyacrylamide, gave rise to one single band. Only alanine was found as N-terminal residue. Carboxypeptidases A and B failed to release any C-terminal residue. The isoelectric point, as determined by isoelectric focusing in polyacrylamide gel slab, was shown to be 4.9-5.0. Non-chromatographed, but not the purified zymogen, could be converted into active thrombin in half-saturated trisodium citrate seeded with thrombin. Pure sheep prothrombin showed 5.6% of neutral sugars and the following amino acid composition: Ala35, Arg44, Asx54-55, -Cys24, Glx72, Gly53-54, His8, Ile19, Leu45, Lys31, Met7, Phe23, Pro36, Ser34, Thr29-29, Trp16, Tyr19 and Val33, which accounts for a molecular weight of about 66 000 (amino acids only). The molecular weight as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis after reduction by 2-mercaptoethanol, was shown to be 77 000 +/- 3000 (carbohydrates included).

Pig prothrombin: purification and properties

A procedure for the preparation of highly purified pig prothrombin is described. Compared to the initial clotting activity of the starting plasma, this protein was purified 776 times with a final yield of 8 per cent. The purified zymogen showed a specific activity of 1,460 NH units/mg of protein , a molecular weight of 65,000 as determined by SDS-polyacrylamide disc gel electroesis, E 1.0 mg/ml 1.0 cm, 280 nm = 1.45 at pH 7.0 and the following amino acid composition: Asx 51, Thr 38, Glx 62, Pro 23, Gly44, Ala 25, Half-Cys 30, Val 35, Met 3, Ile 30, Leu 32, Tyr 19, Phe 22, Lys 36, His 8, Arg 28, and Trp 13, which accounts for a minimum molecular weight of 59,370 (carbohydrates not computed). Alanine was found as the only N-terminal residue. Carboxypeptidases A and B failed to release any C-terminal residue. By hydrazinolysis however 0.4 mole of serine was released per mole of prothrombin. The activation of crude and chromatographed pig prothrombin was investigated.

Purification of human blood clotting factor X by Blue Dextran agarose affinity chromatography

Blue Dextran 2000 coupled covalently to agarose has been used as an affinity column for the rapid separation of human blood clotting Factor X. Factor X has been isolated with approximately 2000-fold purification from human citrated plasma and shows single-component behavior by sodium dodecyl sulfate gel electrophoresis. Affinity columns prepared with Blue Dextran chromophore (Cibacron blue) derivatized to agarose or Sepharose gave negative results. These studies have shown that Blue Dextran agarose possesses unique biospecific and nonbiospecific properties, both of which are essential to achieve resolution of Factor X from other vitamin K-dependent blood clotting factors.

Improved procedures for the purification of selected vitamin K-dependent proteins

Improved methods are described to obtain bovine prothrombin, Factor IX, Protein C, and autoprothrombin III (Factor X, Auto-III) in purified form. The prothrombin had a specific activity of 4,340 Iowa units/mg. Theoretically, a preparation of clean thrombin should have a specific activity of 8,200 U/mg, because 47.08% of the protein in prothrombin is lost when thrombin forms. Such thrombin preparations have been obtained (Arch. Biochem. Biophys. 121, 372 (1967)). The prothrombin concentration of bovine plasma is near 60 mg/liter. Protein C, first isolated by Stenflo (J. Biol. Chem. 251, 355 (1976)), was found to be the precursor of autoprothrombin II-A (Auto-II-A), discovered earlier (Thromb. Diath. Haemorrh. 5, 218 (1960)). Protein C (Factor XIV) was converted to Auto-II-A (Factor XIVa) by thrombin. Digesting purified Auto-III with purified thrombin removed a small glycopeptide from the COOH-terminal end of the heavy chain to yield Auto-IIIm. Auto-III thrombin leads to Auto-IIIm + peptide. Auto-IIIm was not converted to the active enzyme with thromboplastin, and furthermore, inhibited the activation of purified native Auto-III with thromboplastin. Auto-IIIm was also not converted to the active enzymes when the procoagulants consisted of purified Factor VIII, purified Factor IXa, platelet factor 3 and calcium ions. The "activation peptide" released by RVV-X from the NH2-terminal end of the heavy chain and the active enzyme (Auto-Cm) were purified. Auto-III was also activated with purified RVV-X. The same "actid of Auto-Cm. Purified Factor IX developed anticoagulant activity when reacted with an optimum concentration of purified thrombin. A suitable reagent for the assay of Factor IX was prepared by removing prothrombin complex from anticoagulated bovine plasma and restoring the prothrombin and Auto-III concentration with use of the respective purified proenzymes.