Characterization of beta-endorphin binding protein (receptor) from rat brain membranes

Rat brain membranes (RBM) bind beta-endorphin with high affinity and specificity. We report herein the identification of a high molecular weight beta-endorphin complex (receptor) in extracts of RBM preincubated with tritiated beta-endorphin, by using the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). Upon isoelectric focusing, this complex gives a single peak with an isoelectric point (+/- SEM) of 4.50 +/- 0.06. Sucrose density gradient experiments in H2O and 2H2O yield effective partial specific volume (v = 0.814 cm3/g and sedimentation constant s20,w = 15.6 S. Gel filtration yields an estimate of the hydrodynamic radius of 73 A. The corresponding frictional ratio of 1.12 is consistent with an elliptical spheroid with an axial ratio of 3.1-3.2. The molecular mass of the complex is estimated to be 690,000 daltons. The v of the complex is greater than that of CHAPS or most globular proteins.