Oryzon Genomics 1 article published in JoVE Biochemistry Direct Measurement of KDM1A Target Engagement Using Chemoprobe-based Immunoassays Cristina Mascaró1, Raquel Ruiz Rodriguez1, Tamara Maes1 1Oryzon Genomics Here, we present a protocol to measure KDM1A target engagement in a human or animal cell, tissue or blood samples treated with KDM1A inhibitors. The protocol employs chemoprobe tagging of the free KDM1A enzyme and direct quantification of the target occupation using chemoprobe-based immunoassays and can be used in preclinical and clinical studies.