beta-Endorphin: characteristics of binding sites in the mouse brain

Binding of human beta-endorphin to mouse brain membrane preparations has been characterized using the tritiated hormone as primary ligand. The binding was shown to be time and temperature dependent. The dissociation constant of the saturable binding was determined to be 0.5 nM. Both [Met5]enkephalin and naloxone were found to compete with tritiated beta-endorphin for the binding with a potency of 6.3 and 6.5% of the unlabeled hormone, respectively. Phospholipase A2 isolated from Formosan cobra venom was shown to be a potent inhibitor of the binding with a 50% inhibition concentration of 26 nM. Although Na+, K+, Ca2+, Mg2+ were found individually to exert a profound inhibition on the binding, the combined salt solution (Tyrode) did not abolish the specific binding of tritiated beta-endorphin to the mouse brain membrane preparations.