Biochemical Characterization of an Isolated and Functionally Reconstituted γ‐Aminobutyric Acid/Benzodiazepine Receptor

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Abstract
We have solubilized, affinity‐purified, and functionally reconstituted the γ‐aminobutyric acid/benzodiazepine (GABA/BDZ) receptor from rat brain into natural brain lipid liposomes. The detergent, 3‐[(3‐cholamidopropyl)‐dimethylammonio] 1‐propanesulphonate, was employed for the isolation of the receptor in the presence of a whole rat brain lipid extract supplemented with cholesteryl hemisuccinate. The soluble and reconstituted protein showed a homogeneous [3H]flunitrazepam binding population and the allosteric modulation of this binding site by GABA, by the pyrazolopyridine, cartazolate, and by the depressant barbiturate, pentobarbital. The purified GABA/BDZ receptor when incorporated into liposomes has been visualized by electron microscopy and reveals rosette structures, 8–9 nm in diameter, which appear to have a central pore. Sodium dodecyl sulphate‐polyacrylamide gel electrophoresis of the reconstituted GABA/BDZ receptor reveals three major protein bands of 41, 52–56, and 59–62 kDa, the latter two of which appear as doublets. Functional receptor reconstitution is demonstrated by the measurement of GABA‐stimulated 36Cl‐ flux into the purified GABA/BDZ receptor incorporated liposomes and its modulation by the BDZs, barbiturates, and pyrazolopyridines.