Column chromatography on Sephadex G-200 of ammonium sulfate preparations of chicken bile and duodenal washings revealed γA in a high molecular weight form with elution immediately after the void volume. γA from intestinal secretions was further purified by recycling chromatography on a Bio-Gel A-5M column. A constant S value was not obtained for the γA, values of 11.9 to 16.2S being recorded under various conditions. The sedimentation coefficient was relatively unaltered by mild reductive procedures with 0.1 M β-mercaptoethanol and 0.005 M dithiothreitol. Serum γA was partially purified by ammonium sulfate precipitation and DEAE chromatography. The majority of serum γA was in a high molecular weight form, eluting from a G-200 column mainly at the void volume. A smaller amount of γA eluted in the 7S region. The addition of 125I-labeled human secretory component (SC) to fresh chicken serum and subsequent sucrose gradient ultracentrifugation resulted in a 10 to 17% shift of radioactive counts to the heavier portions of the gradients. Radioautography of these fractions with heavy chain specific antisera revealed binding to γA in 3/3, to γM in 1/3 and to γG in 0/3 experiments. Addition of human SC to biliary γA did not result in binding to the γA molecule. This suggests that chicken γA obtained from secretions may possess its own form of SC.
This work was supported by the Medical Research Council of Canada.