Method used to isolate secretory component from secretory immunoglobulin A

An attempt was made to isolate secretory component from the molecule secretory Immunoglobulin A. Two methods were used, each with colostrum as the source of secretory component. In the first method, colostrum was centrifuged, and the supernatant was chromatographed on a Sephadex G-200 column. Half of the eluates were concentrated by negative pressure dialysis, and half of the eluates were chromatographed on a carboxymethyl-50 cation exchange column. All eluates collected were subjected to Immunoelectrophoresis. In the second method the colostrum was clarified, and the proteins were precipitated by the addition of ammonium sulfate. The eluates were chromatographed on a DEAE cellulose column using a stepwise elution of three sodium phosphate buffers. Further chromatography included a GM-50 cation exchange column and identification of the proteins by the method of Ouchterlony using rabbit antiserum against secretory IgA. Free or unattached secretory component was found in the second elution peaks from the Sephadex G-200 gel filtration column and from the first fraction of colostral whey eluted using O.OIM sodium phosphate buffer, at pH 7.6. Secretory component was highly contaminated with lactoferrln and was not obtained In a pure state. Failure to obtain spurring between second peak eluates and antl S-IgA could be the result of differences in quarternary structure between the tetramerlc free form and the IgA bound form.