The fluorescent enkephalins in which an essential Tyr1 residue is replaced by L-1-pyrenylalanine (Pya) were synthesized and examined in the receptor binding assays. [Pya1, Leu5]Enkephalin and its methyl ester showed binding characteristics specific for the opiate receptors, exhibiting a potent inhibition of Tyr1-containing enkephalins. Surprisingly, the methyl ester displayed almost the same potencies to those of DAGO-enkephalin. This analog bound 24-fold more strongly to mu than to delta-receptors. C-terminal free analog Pya1-Enk-OH was delta-preferential with a fairly good affinity. These results indicate that Tyr1 in enkephalin is not necessary to recognition of the opiate receptors.
Alanine Animals