Peptide subunits of gamma-aminobutyric acidA/benzodiazepine receptors from bovine cerebral cortex.

The gamma-aminobutyric acidA/benzodiazepine receptor complexes from bovine cerebral cortex were purified by immunoaffinity chromatography, and the main component peptide subunits were characterized. The peptide band originally thought to be a single beta subunit [57,000 Mr band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)] is composed of at least four different peptides of 54,000-57,000 Mr. Two peptides of 55,000 and 57,000 Mr were recognized by the beta subunit-specific monoclonal antibody 62-3G1. Peptides in the range of 54,000-57,000 Mr were photoaffinity-labeled with [3H]muscimol. A different 57,000 Mr peptide was photoaffinity-labeled by [3H]flunitrazepam, but neither was recognized by the monoclonal antibody 62-3G1 nor photoaffinity-labeled with [3H]muscimol. Some peptides could be identified by their differential mobility shift in SDS-PAGE after treatment with endoglycosidase H. Two additional subunit peptides of 51,000 and 53,000 Mr were also photoaffinity-labeled by [3H]flunitrazepam and reacted with antiserum A. However, the 57,000 Mr peptide that also was photoaffinity-labeled by [3H]flunitrazepam did not react with antiserum A.