Unexpected biotinylation using ATP-γ-Biotin-LC-PEO-amine as a kinase substrate

► Discovery that a biotin-modified ATP reagent biotinylates proteins independent of kinase activity. ► This commercially available reagent cannot be used for phosphoproteomics, as designed. ► Uncovers the flaws in a commercially available reagent. ► the need for control experiments in developing activity-based enzyme probes.