Comparison of combinatorial peptide library screening, proteome-derived library, and ProPeL motif discovery methodologies.

*<p>Phosphorylatable residues (Ser and Thr) and Cys are not included in combinatorial peptide libraries used for kinase specificity determination.</p>**<p>In proteome-derived libraries motif width limits depend on whether the kinase reaction is performed before or after proteolytic peptide digestion.