PAK is activated during platelet spreading on surfaces coated with collagen or TS2/16.

Washed platelets were added to collagen- (A) or TS2/16-coated (B) dishes and incubated at 30°C for the indicated time frame. After removing unbound platelets, reactions were terminated with a lysis buffer, and PAK was isolated by immunoprecipitation with anti-PAK antibody. In some experiments, an anti-PAK antibody was incubated with blocking peptides before immunoprecipitation (A, lower panel). The immunoprecipitates were then subjected to in vitro kinase assays with myelin basic protein as an exogenous substrate. The data are representative of at least 3 experiments.