Fractionation of plasma globulin for prothrombin, thrombokinase, and accessory thromboplastin

Factor Xa: Thrombokinase from Paul Morawitz to J Haskell Milstone

In 1904 Paul Morawitz postulated that an enzyme, which he named thrombokinase, would be the primary activator of prothrombin. Fifty years passed before J Haskell Milstone isolated, purified and functionally characterized the enzyme we now call Factor Xa. This essay summarizes Milstone's work on thrombokinase, and finds context for why his efforts succeeded while others struggled.

The phospholipid requirement of tissue factor in blood coagulation

Using a coagulation assay specific for tissue factor, we found that removal of 95% of the tissue factor-phospholipid resulted in a loss of 98% of its biological activity. The activity could be restored, with yields in excess of 100% by combining the extracted tissue factor with either mixed brain phospholipids or highly purified phospholipids. Phosphatidylethanolamine was the most active, followed by phosphatidylcholine. Phosphatidylserine, phosphatidylinositol, and sphingomyelin had little or no activity. In addition, a requirement for unsaturation and the presence of two fatty acids was demonstrated. The activity of phosphatidylcholine was also dependent on the presence of the base. Furthermore, it was shown that activity was not a function of binding of phospholipids to tissue factor, as both active and inactive lipids were equally bound.

Preparation of thrombokinase from bovine plasma

Thrombokinase is prepared from bovine plasma by a procedure involving: treatment with diatomaceous silica, adsorption on barium sulfate, flowing elution with two successive phosphate buffers, ammonium sulfate fractionation, "spontaneous" activation in concentrated solution, and isoelectric precipitation. The yield of nitrogen is 0.002 per cent, corresponding to 1.2 mg. protein per liter of plasma. When diluted back to the volume of parent plasma, and complemented by calcium plus cephalin, the product causes appreciable activation of prothrombin in 1 minute. Thus, the quantity of thrombokinase obtainable is compatible with a physiologic role. In the more complex system used for routine assay, thrombokinase can be supplied by crude plasma at a dilution of 1/500. In parallel tests, the product appears to be more active than its parent plasma, although it contains only 0.002 per cent of the nitrogen. However, the thrombokinase of the product has been activated, whereas the thrombokinase of the plasma is probably in an inactive precursor state. When diluted back to the volume of parent plasma, to a concentration of 0.2 microgram nitrogen per ml., thrombokinase can slowly activate prothrombin in the presence of oxalate, and without the addition of accessory factors. Activation of prothrombin in the presence of oxalate is faster with higher concentrations of thrombokinase.

Thrombokinase of the blood as trypsin-like enzyme

Thrombokinase of the blood, while resembling enterokinase in its role of activator, is more closely analogous to trypsin in its intrinsic origin. It probably arises from a plasma precursor; but it is different from plasmin (fibrinolysin). Like trypsin, thrombokinase can activate prothrombin without the aid of other factors; however, it is potentiated by platelets plus calcium. Unlike certain tissue "thromboplastins," it does not sediment appreciably in 2 hours at 85,000 g. Like trypsin, it hydrolyzes p-toluenesulfonylarginine methyl ester (TAMe). Chromatography on DEAE-cellulose separated thrombin from thrombokinase. The TAMe esterase associated with the thrombokinase fractions was largely suppressed by soybean trypsin inhibitor, while that associated with the thrombin fractions was not. Highly purified thrombokinase was used as starting material; and thrombokinase was eluted in the last major protein band. Under these conditions stepwise elution was as effective as gradient in leading to further purification. The product of 199 liters of bovine plasma was chromatographed in 1 day; and the specific activity was comparable to that attained previously by repeated electrophoretic fractionations. The assembled data suggest that the thrombokinase protein may be approaching homogeneity.

OUTSTANDING CHARACTERISTICS OF THROMBOKINASE ISOLATED FROM BOVINE PLASMA

Thrombokinase has been isolated from bovine plasma by a procedure which begins with the highly purified product of a previously described method, chromatographs it on DEAE-cellulose, and then fractionates it by continuous flow electrophoresis, yielding 0.2 mg per liter of oxalated plasma. The electrophoretic fraction has shown a single boundary in the ultracentrifuge; and its esterase activity on toluenesulfonylarginine methyl ester has been about the same as that of thrombokinase previously isolated by repeated electrophoretic fractionations. Thrombokinase is a euglobulin with minimum solubility near pH 5.0. It is most stable within the pH range 7.5 to 9.5; but there is also a peak in the stability curve near pH 1.8. A few micrograms of thrombokinase per milliliter can activate prothrombin in the presence of EDTA. A few thousandths of a microgram causes rapid production of thrombin in the system: prothrombin, thrombokinase, calcium chloride, phosphatide, "accelerator." But, thrombokinase has less than 1/175 the proteolytic activity of crystallized trypsin.

PURIFICATION AND SOME PROPERTIES OF AUTOPROTHROMBIN C

Methods were developed for the isolation of autoprothrombin C, which is the second enzyme obtained from purified bovine prothrombin. In the presence of lipids and standardized conditions 0.35 μg of the purified autoprothrombin C were sufficient for clotting recalcified plasma in 15 seconds. Some physicochemical properties are as follows: S20, w is 2.27S, the diffusion constant 8.4 × 10−7 cm2/second, and the partial specific volume 0.695. The molecular weight from physicochemical measurements was 21,500. All amino acids were found, but only 1 molecule of methionine. On the basis of amino acid composition the molecular weight was found to be 27,000, giving an average of 24,200 for our two determinations. Prothrombin contains sufficient of each amino acid residue to supply autoprothrombin C and thrombin. Autoprothrombin II, however, has only sufficient amino acids for either autoprothrombin C or thrombin, but not both. The purified autoprothrombin C contained 7% carbohydrate (orcinol) and 3.8% hexosamine. It was stable at pH 7.2 for more than a week at room temperature, and longer in subzero glycerol solution. Autoprothrombin C was used to obtain a single precipitin band in agar diffusion plates with antibody to prothrombin. The band also identified with a single plasma antibody.

PURIFICATION AND SOME PROPERTIES OF AUTOPROTHROMBIN C

Methods were developed for the isolation of autoprothrombin C, which is the second enzyme obtained from purified bovine prothrombin. In the presence of lipids and standardized conditions 0.35 μg of the purified autoprothrombin C were sufficient for clotting recalcified plasma in 15 seconds. Some physicochemical properties are as follows: S20, w is 2.27S, the diffusion constant 8.4 × 10−7 cm2/second, and the partial specific volume 0.695. The molecular weight from physicochemical measurements was 21,500. All amino acids were found, but only 1 molecule of methionine. On the basis of amino acid composition the molecular weight was found to be 27,000, giving an average of 24,200 for our two determinations. Prothrombin contains sufficient of each amino acid residue to supply autoprothrombin C and thrombin. Autoprothrombin II, however, has only sufficient amino acids for either autoprothrombin C or thrombin, but not both. The purified autoprothrombin C contained 7% carbohydrate (orcinol) and 3.8% hexosamine. It was stable at pH 7.2 for more than a week at room temperature, and longer in subzero glycerol solution. Autoprothrombin C was used to obtain a single precipitin band in agar diffusion plates with antibody to prothrombin. The band also identified with a single plasma antibody.

AUTOPROTHROMBIN C: A SECOND ENZYME FROM PROTHROMBIN

In addition to thrombin, there is another derivative of prothrombin which is an end product of prothrombin activation. It is an accelerator of prothrombin activation, and is called autoprothrombin C. The activity develops from purified bovine prothrombin in 25% sodium citrate solution simultaneously with thrombin. It has been separated from thrombin by chromatography on Amberlite IRC-50 under the conditions previously used for the isolation of thrombin. The fraction which separates from thrombin has esterase activity and very likely this esterase activity is associated with the autoprothrombin C molecule. Since the autoprothrombin C and the thrombin are both derived from prothrombin, at least two enzymes are the end products of prothrombin activation. Autoprothrombin C catalyzed the activation of purified prothrombin in 25% sodium citrate solution, and this function was easily inhibited with p-toluenesulphonyl-L-arginine methyl ester. Autoprothrombin C preparations were mixed with platelets, Ac-globulin, and calcium ions to obtain rapid conversion of purified prothrombin to thrombin. This activation mixture did not generate autoprothrombin C and some unspecified substance most likely needs to be added in order to obtain the autoprothrombin C activity. The activity developed together with thrombin when tissue extracts, Ac-globulin, and calcium ions were used for the activation of prothrombin. Autoprothrombin C is relatively stable over the pH range 5.5 to 8.5. It is stable up to 56 °C for 30 minutes. Plasma contains a substance that inactivates autoprothrombin C.

AUTOPROTHROMBIN C: A SECOND ENZYME FROM PROTHROMBIN

In addition to thrombin, there is another derivative of prothrombin which is an end product of prothrombin activation. It is an accelerator of prothrombin activation, and is called autoprothrombin C. The activity develops from purified bovine prothrombin in 25% sodium citrate solution simultaneously with thrombin. It has been separated from thrombin by chromatography on Amberlite IRC-50 under the conditions previously used for the isolation of thrombin. The fraction which separates from thrombin has esterase activity and very likely this esterase activity is associated with the autoprothrombin C molecule. Since the autoprothrombin C and the thrombin are both derived from prothrombin, at least two enzymes are the end products of prothrombin activation. Autoprothrombin C catalyzed the activation of purified prothrombin in 25% sodium citrate solution, and this function was easily inhibited with p-toluenesulphonyl-L-arginine methyl ester. Autoprothrombin C preparations were mixed with platelets, Ac-globulin, and calcium ions to obtain rapid conversion of purified prothrombin to thrombin. This activation mixture did not generate autoprothrombin C and some unspecified substance most likely needs to be added in order to obtain the autoprothrombin C activity. The activity developed together with thrombin when tissue extracts, Ac-globulin, and calcium ions were used for the activation of prothrombin. Autoprothrombin C is relatively stable over the pH range 5.5 to 8.5. It is stable up to 56 °C for 30 minutes. Plasma contains a substance that inactivates autoprothrombin C.

Chromatography of blood-clotting factors and serum proteins on columns of diatomaceous earth

1. In batch adsorptions with prothrombin solutions, hyflo was the weakest adsorbent, standard super-cel intermediate, and filter-cel strongest. Of these three grades of diatomaceous earth, hyflo has the smallest surface area per gram and filter-cel the largest. In parallel breakthrough experiments, a column of standard super-cel had a capacity almost six times that of a hyflo column. 2. After partial removal of impurities by diatomaceous earth, prothrombin preparations contained less thrombokinase, were more stable, and displayed less tendency to form thrombin "spontaneously." Thrombokinase (or its precursor) was removed from a preparation of prothrombin by passage through a filter cake of standard super-cel. The specific activity of the prothrombin was increased; and 62 per cent of the activity was recovered. 3. Prothrombin was adsorbed from an ammonium sulfate solution at pH 5.26 by columns of hyflo or standard super-cel. When eluted by phosphate solutions, the protein moved down the columns more readily at higher pH and higher concentration of phosphate salts, within the pH range 5.0 to 6.6, and within the phosphate range 0.1 to 1.0 M. 4. Thrombin was adsorbed on a column of standard super-cel at pH 5.11. As successive eluents passed through the column, the thrombin emerged between two bands of impurities. The specific activity of the thrombin was raised; and 83 per cent of the activity was recovered. 5. With a column of standard super-cel, and with a series of eluents within the pH range 5.1 to 6.3, total serum proteins were separated into four major bands. About 94 per cent of the protein was recovered.