Peptide Competition Lysates prepared from NIH3T3 cells left untreated (1) or treated with PDGF (2-5). were resolved by SDS-PAGE on a 10% polyacrylamide gel and transferred to PVDF. Membranes were blocked with a 5% BSA-TBST buffer for one hour at room temperature and incubated with ab12863 antibody for two hours at room temperature in a 3% BSA-TBST buffer, following prior incubation with: no peptide (1, 2), the non-phosphopeptide corresponding to the immunogen (3), a generic phosphosotyrosine containing peptide (4), the phosphopeptide immunogen (5). After washing, membranes were incubated with goat F(ab)2 anti-rabbit IgG HRP conjugate and bands were detected using the Pierce SuperSignal method. The data show that only the peptide corresponding to ab12863 blocks the signal, verifying the specificity of the antibody.