TCEP-biotin is biotinylated form of the reducing agent TCEP and an affinity probe for protein lysine crotonylation. Covalent addition of the TCEP moiety to crotonylated lysine residues results in adduct formation that allows for detection or immobilization of crotonylated proteins through interaction with the biotin ligand. It has been used in the detection and isolation of crotonylated histones in HEK293 cells.