Pharmacological and biochemical characteristics of partially purified GABA receptor

Pharmacological and biochemical characteristics of the partially purified γ-aminobutyric acid (GABA) receptor using baclofen affinity column chromatography have been examined. The Scatchard analysis of [H]GABA binding to the purified GABA receptor showed a linear relationship and the K and B values were 60 nM and 118 pmol/mg of protein, respectively. Although GTP and Mg did not affect on the GABA receptor binding, Ca significantly increased [H]GABA binding to the purified GABA receptor in a dose-dependent manner and showed its maximum effect at 2 mM. The enhancement of the binding by Ca was found to be due to the increase of Bmax by the Scatchard analysis. The treatments with pronase and trypsin significantly decreased the binding of [H]GABA, but phospholipase A had no significant effect on the binding. In addition, treatment with glycosidases such as glycopeptidase A and β-galactosidase significantly decreased the binding of [H]GABA to the purified GABA receptor. These results suggest that purification of the solubilized GABA receptor by the affinity column chromatography may result in the functional uncoupling of GABA receptor with GTP-binding protein. Furthermore, the present results suggest that cerebral GABA receptor may be a glycoprotein and membrane phospholipids susceptible to phospholipase A treatment may not be involved in the exhibition of the binding activity. © 1991 Plenum Publishing Corporation.