Elution of antithrombin from heparin-Sepharose. Antithrombin from proband (A) and normal (B) plasmas was isolated either by a single-step (“Total AT”) or a gradient increase in NaCl concentration. Fractions were collected and analyzed by immunoblotting, as described in Materials and Methods. For fractions collected by gradient elution, the molar concentration of NaCl required for their elution is indicated.