Abstract:  A mouse κ opioid receptor was engineered to contain a FLAG epitope at the amino-terminus to facilitate purification. Selection of transfected human embryonic kidney 293 cells yielded a cell line that expressed the receptor with a B_max of 2 pmoles/mg protein. The κ receptor was solubilized from HEK 293 cell membranes with n-dodecyl-β-D-maltoside. Sequential use of Sephacryl S300 gel filtration chromatography, wheat germ agglutinin (WGA)-agarose chromatography, immunoaffinity chromatography, and SDS/PAGE permitted purification of the receptor. MALDI-TOF mass spectrometry was used to identify and characterize peptides derived from the κ opioid receptor following in-gel digestion with trypsin, and precursor-derived ms/ms confirmed the identity of peptides derived from enzymatic digestion of the κ opioid receptor.