Isolation and characterization of a hereditary abnormal antithrombin III 'Antithrombin III Toyama'

A hereditary abnormal antithrombin III (AT-III) 'Antithrombin III Toyama' was purified from the plasma of a patient with recurrent thrombophlebitis by a procedure involving barium chloride and ammonium sulfate fractionations, affinity chromatography on anti-AT-III-Sepharose gel, and DEAE-Sephadex chromatography. Purified abnormal AT-III was shown to be the same as normal one in the molecular size, having the same molecular weight, amino-terminal sequence and carboxy-terminal amino acid. Abnormal AT-III gave the same UV spectrum as normal AT-III and both proteins were immunologically identical. Abnormal AT-III, however, showed the different electrophoretic mobility on agarose gel electrophoresis and immunoelectrophoresis. Abnormal AT-III was more electronegative than normal one, before and after a neuraminidase digestion of both proteins. These results suggest that in antithrombin III Toyama an amino acid residue at the heparin-binding site has been replaced by less basic or more acidic one which has no ability to interact with heparin, resulting in a loss of heparin cofactor activity of this protein.