PP1 inhibits Lyn kinase activity but not c-Kit kinase activity in MO7e cells. MO7e cells were treated for 30 minutes at 37°C in the presence or absence of PP1 (10 μmol/L). The cells were then lysed and assessed for either Lyn or c-Kit activity as described in the Materials and Methods section. (A) Lyn kinase activity is inhibited after treatment with PP1. Immune complex assays were performed on Lyn immunoprecipitated from cell lysates, resolved with SDS-PAGE, transferred to Immobilon, and radiolabeled Lyn was visualized with autoradiography. (B) Equivalent amounts of Lyn protein are present in the immune complex kinase assays. Immunoblotting with Lyn-specific antibody was performed on the immunoprecipitates shown in Panel A. (C) PP1 does not impair c-Kit kinase activity. Immune complex assays were performed on c-Kit immunoprecipitated from cell lysates, resolved with SDS-PAGE, transferred to Immobilon, and radiolabeled c-Kit was visualized with autoradiography. (D) c-Kit immunoblot of Panel C.