Comparative kinetics of tyrosine phosphorylation of cortactin in control, thrombasthenic, and RGDS-treated platelets. Platelets from a control (CONTROL), the type II thrombasthenic patient (PATIENT) of Fig 1B (top panel), or control platelets incubated with 1 mmol/L RGDS peptide (RGDS) (lower panel) were activated with 0.05 U/mL thrombin, solubilized, and immunoprecipitated with an anticortactin antibody (IP: cortactin). Immunoprecipitated polypeptides were subjected to SDS-PAGE followed by Western blot analysis using an anti-Ptyr antibody (“anti-Ptyr” in the “Blot” column) or an anticortactin (“anticortactin” in the “Blot” column) to control for efficiency of cortactin immunoprecipitation (shown only for upper panel). Aggregation rates are indicated.