OPIOID ACTIVITIES OF FRAGMENTS OF BETA-ENDORPHIN AND OF ITS LEUCINE-65-ANALOG - COMPARISON OF THE BINDING-PROPERTIES OF METHIONINE-ENKEPHALIN AND LEUCINE-ENKEPHALIN

For characterisation in vitro, four parallel assays were used: the guinea pig ileum and mouse vas deference as pharmacological models at 36°C and the inhibition of binding of [3H]-leucine-enkephalin and [3H]-methionine-enkephalin at 0°C. The Leu65-analogue of β-endorphin and its pragments (61-65, 61-76 and 61-77) have a lower affinity to the [3H]-naltrexone binding site or μ-receptors than the corresponding Met65-peptides whereas no such difference was found for the [3H]leucine-enkephalin binding sites or δ-receptors. When the binding of [3H]-methionine-enkephalin or [3H]-leucine-enkephalin was inhibited by cold ligands interacting with δ-, μ-, or κ-receptors, no evidence was obtained for more than one type of δ-binding site. © 1979.