Fig. 2.
Src-mediated activation of Btk in collagen-treated platelets.
(A) Platelets were treated with collagen as in Figure 1A for the time indicated. Btk was purified from the soluble extracts by immunoprecipitation as described above, then immunoblotted with Btk phosphopeptide site-specific antibodies 551PY (top panel) and 223PY (middle panel) or anti-Btk antibody (bottom panel). (B) Platelets were treated with either collagen or buffer for 1 minute. Btk was purified from the soluble extracts by immunoprecipitation as described above. The immune complexes were incubated in a kinase buffer containing [γ-32P]ATP for 5 minutes as described in “Materials and methods.” Incorporation of 32P into Btk was visualized by autoradiography.
