Identification of mammalian brain and spinal cord opioid receptor by photoaffinity labeling

A radioiodinated photoreactive enkephalin derivative, 125I(D-Ala2, p-N3-Phe4-Met5)enkephalin, was used to photoaffinity label the opioid receptor from the membranes of four mammalian brains (without cerebellum) and spinal cords. These included the cat, rabbit, guinea pig and mouse. The photolabeled membranes were analyzed by sodium dodecyl sulfate gel electrophoresis. A 43,000-daltons protein was specifically photolabeled in all the membranes tested, as the specific labeling of this protein was inhibited in the presence of 14.5 microM of (D-Ala2, Met5)enkephalin. These data suggest that the 43,000-daltons protein is a binding protein of the opioid receptor in the different mammalian neural tissues.