Co-immunoprecipitation of protein kinase activity with CD63. Panel A, Cells were solubilized in Brij solubilization buffer and immunoprecipitated with NMS (lane 1), the CD63 mAb AHN-16 (lane 2), or the anti-MCSP mAb 9.2.27 (lane 3), and the immunoprecipitates were incubated with [γ-32P]ATP as described in the text. The resulting phosphoproteins were resolved by SDS-PAGE and visualized by autoradiography as described in the text. Three phosphoproteins were reproducibly identified in CD63 mAb immunoprecipitates (labeled 1–3 in lane 2). One phosphoprotein was reproducibly identified in immunoprecipitates using the anti-MCSP mAb 9.2.27 (labeled 4 in lane 3). These four phosphoproteins were not seen in the immunoprecipitate using NMS (lane 1). Proteins used as molecular weight standards were: myosin heavy chain, 200,000; Escherichia coli β-galactosidase, 116,000; bovine serum albumin, 66,000; ovalbumin, 45,000; and carbonic anhydrase, 29,000.