Mouse brain opioid receptor identification by direct ultraviolet photoaffinity labeling.
[3H]Morphine, PL-017[prolyl-3,4-3H,D-prolyl,3,4-3H] ([3H]PL-017) and enkephalin-(2-D-penicillamine,5-D-penicillamine)[tyrosyl-2,6-3H] ([3H]DPDPE) were directly cross-linked to mouse brain opiate receptors by an ultraviolet (254 nm) irradiation procedure. [3H]Morphine preferentially and specifically labeled a 58 kDa protein. The labeling of this protein was suppressed by the addition of excess naloxone. Dithiothreitol reduced the irreversible binding of [3H]morphine and [3H]PL-017 to the receptor protein. In the acid hydrolysate of [3H]DPDPE-labeled opiate receptors, dityrosine, was detected. These results suggest that the [3H]tyrosine residue of [3H]DPDPE covalently bound the tyrosine residue of delta-opioid receptors. The direct UV-photoaffinity labeling method using commercially available radioactive opiates described here should be a useful tool for characterization and purification of the opiate receptors.