pp125^FAK phosphorylation. (A) 24/12 cells (lanes 1 through 3) or AM-1 cells (lanes 4 through 6) were maintained in suspension for 15 minutes with no addition (S; lanes 1 and 4), with the addition of 250 μg/mL of fibrinogen (S, Fg; lanes 2 and 5), and with addition of fibrinogen and 10 μg/mL of Fab fragments of PT25-2 (S, Fg+PT; lanes 3 and 6). (B) 24/12 cells (lanes 1 through 3) or AM-1 cells (lanes 4 through 6) were allowed to become adherent to immobilized fibrinogen (Fg; lanes 3 and 6) or poly-L lysine (PL; lanes 2 and 5) or were maintained in suspension (S; lanes 1 and 4) for 30 minutes. The cells were lysed and pp125^FAK was immunoprecipitated with an anti-FAK polyclonal antibody. Phosphotyrosine was detected with 4G10 (upper panel), and blots were reprobed with anti-FAK to assess gel loading (lower panel).