Measurement of p42^mapk and p44^mapk induced by botrocetin-vWF. Platelets (10⁹/mL) were stimulated with 1 U/mL of thrombin or 3 μg/mL of botrocetin and 10 μg/mL of vWF for the indicated time intervals, and reactions were terminated with an equal volume of SDS sample buffer. Samples were boiled for 5 minutes and diluted 40-fold with Tris-buffered saline. p42^mapk was immunoprecipitated using anti-p42^mapk MoAb and the immunoprecipitates were subjected to electrophoresis on 10% SDS-PAGE gels containing 0.5 mg/mL of MBP. The MAP kinase in gel was then renatured, and the gels were incubated with the kinase assay buffer containing [γ-³²P]ATP. The autoradiograph shows the band of renatured p42^mapk activity. The data are representative of three experiments.