Solubilization and affinity purification of the alpha 2-macroglobulin receptor from human fibroblasts

Plasma membranes showing specific binding of alpha 2-macroglobulin (alpha 2M) complexes were isolated from normal human fibroblasts. The membrane preparation was solubilized with Triton X-100, and specific binding to solubilized receptor was demonstrated by precipitation of the alpha 2M X protease receptor complexes with polyethylene glycol. The solubilized receptor could be quantitatively adsorbed on immobilized alpha 2M complexes. Adsorbed receptor was then dissociated from the alpha 2M complexes with either EDTA, bacitracin, the monoclonal anti-receptor-recognition site antibody F2B2 , or low pH. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the affinity-purified receptor preparation revealed polypeptides of 360, 130, and 83 kDa.