Various proteins from rat brain, specifically and irreversibly labeled by [3H]flunitrazepam, are distinct alpha-subunits of the GABA-benzodiazepine receptor complex.

gamma-Aminobutyric acid (GABA)-benzodiazepine receptors were purified from the brains of 5 to 10-day-old rats and photolabeled by [3H]flunitrazepam. After sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), 3 different proteins with apparent molecular weight 51,000, 53,000 and 59,000 Da specifically and irreversibly labeled by [3H]flunitrazepam were revealed by autoradiography. The same 3 proteins were recognized by the alpha-subunit-specific monoclonal antibody bd-28. In contrast, a different protein with apparent molecular weight 56,000 Da was recognized by the beta-subunit-specific antibody bd-17. These results indicate that the various proteins specifically labeled by [3H]flunitrazepam are different alpha-subunits and distinct and different from the beta-subunit of the GABA-benzodiazepine receptor complex.