Max-Planck-Institut fur Hirnforschung 1 article published in JoVE Neuroscience Cell-Type Specific Protein Purification and Identification from Complex Tissues Using a Mutant Methionine tRNA Synthetase Mouse Line Belquis Nassim-Assir1, Daniel Ouro Corredera2, Rodrigo Alvarez-Pardo2, Susanne tom Dieck1, Elena Ciirdaeva1, Erin M. Schuman1, Beatriz Alvarez-Castelao2 1Max-Planck-Institute for Brain Research, Synaptic Plasticity Department, 2Department of Biochemistry and Molecular Biology, Veterinary School, Complutense University of Madrid This protocol describes how to perform cell-type-specific protein labeling with azidonorleucine (ANL) using a mouse line expressing a mutant L274G-Methionine tRNA synthetase (MetRS*) and the necessary steps for labeled cell-type-specific proteins isolation. We outline two possible ANL administration routes in live mice by (1) drinking water and (2) intraperitoneal injections.