Effects of GRGDS peptide plus EGTA on p72^syk-associated tyrosine kinase activity induced by botrocetin-vWF. Platelets were incubated with or without 200 μmol/L GRGDS peptide plus 1 mmol/L EGTA (instead of Ca²⁺) for 5 minutes and then activated with 3 μg/mL of botrocetin and 10 μg/mL of vWF for the indicated time intervals. For analysis of p72^syk autophosphorylation, reactions were terminated by adding lysis buffer. p72^syk was immunoprecipitated with anti-p72^syk MoAb, and the sample was Western-blotted using antiphosphotyrosine MoAb, 4G10. The arrowhead represents the band presumably derived from IgG heavy chains. The data are representative of three experiments.