A M r 58 000 subunit of the opiate receptor has been identified using tritiated fentanyl isothiocyanate, a potent opiate alkylating reagent with specificity for the δ-opiate receptor subclass. The subunit is alkylated in the presence of dextrorphan but not levorphanol. The specifically labelled protein was retained on columns of immobilized wheat germ agglutinin and is therefore presumably a glycoprotein. Partial purification of the M r 58 000 opiate receptor subunit from neuroblastoma × glioma NG108-15 hybrid cell membranes is described.
