Fig. 7. CD activates pp60^c-src kinase activity. Cells were incubated in 10 µM CD and extracts prepared at the times indicated for the immune complex assay of pp60^c-src activity. Autophosphorylated pp60^c-src kinase and phosphorylated IgG heavy chain were evident at 7.5 minutes after CD addition and maximal at 15 minutes post-stimulation (A). Kinase activity rapidly declined thereafter. Addition of PP1 to cultures prior to CD treatment effectively inhibited pp60^c-src kinase activity at the optimal 15 minute time point. Equal gel loading was confirmed by visualization of the IgG heavy chain by staining with Ponceau S (B) and by western blotting for pp60^c-src and IgG (C). The histogram indicates quantitative data (mean±s.d.) for three independent experiments.