University of New Mexico School of Medicine 1 article published in JoVE Biochemistry An Optimized Single-Molecule Pull-Down Assay for Quantification of Protein Phosphorylation Elizabeth M. Bailey1, Emanuel Salazar-Cavazos1, Rachel M. Grattan1, Michael J. Wester2, David J. Schodt2, Julian A. Rojo1, Keith A. Lidke2,3, Diane S. Lidke1,3 1Department of Pathology, University of New Mexico School of Medicine, 2Department of Physics and Astronomy, University of New Mexico, 3Comprehensive Cancer Center, University of New Mexico Health Sciences Center The present protocol describes sample preparation and data analysis to quantify protein phosphorylation using an improved single-molecule pull-down (SiMPull) assay.