Effect of human B-endorphin on the binding of different opiates to mouse brain membranes

The competition of human B-endorphin (B-EP) for dihydromorphine (DHM) and D-Ala2-D-Leu5-enkephalin (DADLE) binding sites has been studied at three temperatures, 0 degree, 25 degrees, and 37 degrees C. B-EP is more effective in inhibiting mu and delta binding at 0 degree and 25 degrees than at 37 degrees C. This difference does not seem related to a temperature-dependent degradation of the peptide. DHM and DADLE high affinity binding sites are clearly distinguished by B-EP. The high affinity site for DHM and the low of DADLE are the more easily displaced by B-EP, but with different affinities. These sites are different in binding capacities, although distinct stoichiometric ratios of binding or the existence of isoreceptors could account for their identity.