HETEROGENEITY IN HUMAN-PROTHROMBIN - ANALYSIS OF CAUSE

  • 1 January 1981
    • journal article
    • research article
    • Vol. 58  (5) , 886-891
Abstract
Two fractions of human prothrombin can be isolated from single donor plasma by the technique of heparin-agarose chromatography in (sodium) citrate buffer, pH 7.5, as previously reported for pooled plasma. The 2 fractions, designated H-II1 and H-II2, are found in a ratio of .apprx. 4:1. Both forms comigrate in sodium dodecyl sulfate gel electrophoresis; under nondenaturing electrophoretic conditions, each fraction migrates as a discrete entity with a different mobility. The larger fraction (H-II1) has a faster mobility towards the anode. Isoelectric focusing in urea of H-II1 reveals that it has 2 components, a minor component with a pI of 5.25 (H-II1a) and a major component with a pI of 5.40 (H-II1b). H-II2 has a pI of 5.6. H-II1 and H-II2 possess the same amino terminal residue (alanine, 0.87-0.92 mol/mol) and the same number of .gamma.-carboxyglutamic acid residues (9.8-10.5). Their amino acid composition is indistinguishable. The 2 fractions of prothrombin differ in their content of neutral sugar and of sialic acid residues. Removal of sialic acid with neuraminidase abolishes the electrophoretic heterogeneity. The charge heterogeneity of the 3 variants of prothrombin found in normal human plasma appears to result exclusively from differences in the number of sialic acid residues attached to the protein moiety of the molecule.