Molecular sizes of photolabeled GABA and benzodiazepine receptor proteins are identical

[3H]Muscimol was irreversibly incorporated into rat cerebellar membranes upon irradiation with ultraviolet light. GABA agonists and antagonists inhibited this incorporation. The reversible muscimol-binding decreased after photoaffinity-labeling of the membranes with muscimol. These results indicated that this irreversible incorporation is to the GABA receptor. Photolabeled GABA receptor protein showed its Mr of 50000 +/- 1000 in SDS-polyacrylamide gel electrophoresis. This molecular size is identical to that of the benzodiazepine receptor which was photolabeled with 3H-flunitrazepam.