Beta-Endorphin. Interaction of synthetic analogs having different chain lengths with morphine and enkephalin receptors in rat brain membranes.

Human beta-endorphin analogs with various chain lengths have been investigated for their potency in displacing tritiated dihydromorphine and Leu-enkephalin binding in rat brain membrane preparations. It was found that the reduction of chain length from residues 1-31 to 1-5 led to a gradual loss of preference for the morphined receptor. In addition, the extension of the chain length of the Met-ekephalin segment to the COOH-terminal glutamic acid modified the binding of the NH2-terminal sequence to the enkephalin receptor. The fact that camel beta-endorphin is more potent in displacing the two tritiated primary ligands than the human hormone is also reported herein.