Fig. 2. Phosphorylation of exogenous FGF-1 in FGFR-transfected cells. (A) COS-1 cells and (B) HeLa cells were transfected with FGFRs as indicated, pretreated with [³³P]phosphate and incubated for 6 hours with FGF-1 or FGF-1 K132E and with heparin where indicated. FGF-1 was extracted from cell lysates as described in Materials and Methods and then separated by SDS-PAGE and blotted onto Immobilon-P membrane. ³³P-phosphorylated FGF-1 was detected by autoradiography (upper panel) and the total cell-associated FGF-1 was detected by anti-FGF-1 antibodies (lower panel).