Degradation of normal and dicoumarol-induced prothrombins with thrombin

Purification and characterization of dicoumarol-induced prothrombins. Evidence of 5-Gla variant with two (or more) polypeptide chains

A 5-Gla prothrombin, adsorbable onto barium oxalate and containing an admixture of one- and two-chain molecules, has been purified from the plasma of steers on a dicoumarol regimen for three years. Double-chain molecules were not detected in any of our six other variants containing zero to nine Gla residues. In this double-chain variant, the peptide bond between Arg52-Asn appears to be missing, as the preparation showed amino-terminal alanine and aspartic acid, and released both double- and single-chain F1 upon digestion with thrombin. The molecular masses of the F1 and its heavy chain were 24,000 and 19,000 daltons, respectively. The double-chain variant was similar to its single-chain counterpart [Malhotra, O.P. (1979) Thromb. Res. 14, 439-448] in that it (a) yielded thrombin equivalent to 30% of normal in three hr, (b) moved in the alpha 1 region in the absence of calcium ions and between the alpha 1 and alpha 2 macroglobulins in the presence of calcium ions, (c) contained five gamma-carboxyglutamyl residues (Gla), and (d) showed comparable antigenic activity with normal prothrombin.

Monoclonal antibodies to prothrombin

Hybridoma technology was used for the production of murine monoclonal antibodies to bovine normal prothrombin. Hybrid cell cultures were assayed for the production of antibodies, both in the absence and presence of calcium ions, by Enzyme-Linked Immunosorbent Assay (ELISA). Antibody-producing cell lines were cloned two times and grown as ascites tumors. Monoclonal antibodies (McAb), isolated by affinity chromatography (Protein A-Sepharose), were tested for their affinity for normal (10-Gla) and dicoumarol-induced abnormal prothrombins containing 2, 5, 7, 8 and 9 gamma-carboxyglutamyl (Gla) residues. A total of 24 McAb were obtained and the immunoglobulins were of the IgG1 subclass. Nine of the twenty-four McAb did not require Ca2+ for the formation of Ag-Ab complexes, and reacted equally with normal and Gla-deficient prothrombins. These antibodies had affinity for prethrombin1 (P1) but not for the Gla-containing prothrombin fragment1 (F1) portion of the molecule. In contrast, the 15 Ca2+-dependent McAb reacted with F1 but not with P1. They discriminated the abnormal prothrombins based upon their Gla content. For example, though all the Ca2+-dependent McAb formed Ag-Ab complexes with 9-, essentially none formed with 5- or less-Gla prothrombins. [Some reacted equally with 9- and 10-Gla (normal) prothrombin while others had only 25% of normal affinity for 9-Gla isomer]. Only four and twelve of the 15 McAb had some affinity for 7- and 8-Gla variants, respectively. These results show that antibodies which react with the Ca2+-stabilized conformation of prothrombin are not specific for normal prothrombin, as has been reported in the literature.

Electroimmunoassay of prothrombin

Electroimmunoassay of normal (10-Gla) and Gla-deficient prothrombins containing 0 to 9 Gla (gamma-carboxyglutamyl) residues performed in EDTA against anti- (normal) prothrombin showed that each of the Gla-deficient proteins contained as much antigenic activity as does the normal molecule. In the presence of Ca2+, however, normal prothrombin appeared to show the least while 0- to 2-Gla variants, the most activity. This anomaly arises from the presence of antibodies (Ca-IIAb) which form antigen-antibody (Ag-Ab) complexes when the conformation of the antigen is stabilized in Ca2+. For example, upon fractionation of the antisera and mixing Ca-IIAb (bound to 10-Gla prothrombin, Affi-gel column and eluted by replacing Ca2+ with EDTA) with those reacting with prethrombin1 (non-Gla portion of the molecule), rocket heights in Ca2+ decreased the most with 10- and 9-Gla (32%), followed by 13% with 8-Gla, 2% with 7-Gla and none with 2-Gla prothrombins--indicating that Ca-IIAb do cross react with 7-, 8- and particularly 9-Gla prothrombins. This was also confirmed by the fact that anti 7-Gla but not anti 0-Gla sera contained some antibodies which reacted only in the presence of Ca2+.

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.