Opioid peptides affinity labels

The chemical structures and biological activities of hundreds of opioid analgesics derived from the prototype opioid drug morphine are most comprehensively described in two books published in 1986, one entitled Opioid Analgesics, Chemistry and Receptors by Casy and Parfitt [1] and the other entitled Opiates by Lenz et al. [2]. Follow-up articles include those by Casy in 1989, entitled Opioid Receptors and their Ligands Recent Developments [3] which also includes sections on opioid peptides, affinity labelling and opioid receptor subtypes Rees and Hunter in 1990 [4] covering the... 

Photoaffinity labels have also been investigated. These are enkephalin analogs containing a photosensitive group [e.g., 4-azidophenyl or 2-nitro-4-azidophenyl (NAP)] that form a covalent bond upon irradiation with UV light. Thus, both the peptide 11<37) and the Leu-enkephalins 12(38) bind strongly to brain membranes on photolysis, and the latter pair have been shown to cause a 20-30% inactivation of opioid receptors. Further work on affinity labels and related topics is described in the 1982 and 1983 reports of the International Narcotics Research Conference/39 ... 

Peptide-based affinity labels have been principally photoaffinity labels, including the azide derivatives of several enkephalin analogs and CTP (see Refs. 286,594 for detailed reviews). As noted earlier (Section 5.11.2), the use of photoaffinity labels, however, has been limited because opioid receptors are susceptible to inactivation by UV irradiation (643). 

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