Molecular Pharmacology, Vol 16, 757-766, Copyright © 1979 by the American Society for Pharmacology and Experimental Therapeutics

Multiple Molecular Forms of Stereospecific Opiate Binding

¹ Department of Pharmacology, University of California, San Francisco, California 94122

When brain membranes were incubated in vitro with ³H-enkephalinamide, then extracted with the non-ionic detergent Brij 36-T, up to 75% of the levorphanol-displaceable radioactivity was released in a bound form. Analysis of the binding material by gel filtration revealed a broad peak of 100,000-500,000 molecular weight, and several other species of less than 20,000 molecular weight. Iso-electric focusing resolved the binding components into two major peaks of pI’s about 8.4 and 3.2, and several minor species in the pI range 8.3-6.5; both high and low molecular weight material appeared to be present in the two major pI peaks. All of the stereospecific binding components identified by iso-electric focusing appeared to behave similarly with respect to several competing unlabeled drugs, and to Na⁺ ion. Comparable heterogeneity was observed in material stereospecifically binding ³H-_H-endorphin, ³H-etorphine, and ³H-naloxone, and incubation of Brij-extracted ³H-H-endorphin-binding membranes with 10 mM dimethyl suberimidate covalently labeled a broad range of species of 2-200 x 10³ molecular weight. These results demonstrate that many distinct brain membrane components can bind opiates stereospecifically in vitro; these components may include lipids as well as proteins.

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ACKNOWLEDGMENT We thank Drs. Richard Houghten and C. H. Li for the gift of tritiated _H-endorphin.