The 110kD association molecule of CD9 is β1 subunit of integrin. (A) MS-5 cells were surface-labeled with biotin, lysed, and then immunoprecipitated with KMC8.8 or KMI6, an anti-β1 antibody. The blot was reacted with avidin-biotin-immunoperoxydase complex and the proteins were visualized using an ECL chemiluminescence system. (B) The cell lysates of MS-5 cells were immunoprecipitated with the indicated antibodies. The blot was probed with biotinylated KMI6, followed by reacting with avidin-biotin-immunoperoxydase complex, and the proteins were visualized using an ECL chemiluminescence system. (C) MS-5 cells were surface-labeled with biotin, lysed, and then immunoprecipitated with KMC8.8 or KMI6. The immunoprecipitates were separated by isoelectric focusing in the first dimension, then subjected to SDS-PAGE in the second dimension. The blot was reacted with avidin-biotin-immunoperoxydase complex, and the proteins were visualized using an ECL chemiluminescence system. The immunoprecipitates by KMC8.8 (left panel) and KMI6 (right panel) were compared.