title: Characterization of complexes containing protein A and rabbit immunoglobulin G or Fc gamma fragments.
abstract: Soluble complexes prepared over a range of molar ratios of [125I] protein A (SpA) and rabbit [131I]immunoglobulin G (IgG) or [131I]Fc gamma fragments were separated by ultracentrifugation in a sucrose gradient and selectively radioimmunoprecipitated with chicken antibodies that bind free or complexed SpA. With excess [125I]SpA the only complexes formed were composed of one molecule of labeled ligand and one molecule of [125I]SpA (1:1 complexes). With excess ligand the only complexes formed corresponded to [(IgG)2SpA]2 or [(Fc gamma)2SpA]2 (4:2 complexes). The 4:2 complex likely is responsible for several of the biological activities associated with SpA, including activation of humoral and cellular immune mechanisms, which are optimal under conditions of excess IgG.
mesh_terms: D000818:Animals; D007141:Immunoglobulin Fc Fragments / Q000032:analysis*; D007128:Immunoglobulin Fragments / Q000032:analysis*; D007074:Immunoglobulin G / Q000032:analysis*; D007202:Indicators and Reagents; D007457:Iodine Radioisotopes; D008970:Molecular Weight; D011233:Precipitin Tests; D011817:Rabbits; D013205:Staphylococcal Protein A / Q000032:analysis*; D014461:Ultracentrifugation
chemical_list: D007141:Immunoglobulin Fc Fragments; D007128:Immunoglobulin Fragments; D007074:Immunoglobulin G; D007202:Indicators and Reagents; D007457:Iodine Radioisotopes; D013205:Staphylococcal Protein A