WB (peptide competition) analysis of A431 cells stimulated with 100 ng/mL PMA (a phorbol ester activator of protein kinase C) for 30 minutes at 37ºC (Lane 2-5) using GTX10697 p90 RSK1 (phospho Ser380) antibody prior incubated with the non-phosphopeptide corresponding to the immunogen (Lane 3), a generic phosphoserine-containing peptide (Lane 4), or, the phosphopeptide immunogen (Lane 5) control. The data show that only the immunogen phosphopeptide blocks the signal, demonstrating the specificity of the antibody.