HETEROMERS OF GLUTAMATE-DECARBOXYLASE ISOFORMS OCCUR IN RAT CEREBELLUM

The subunit structure of brain glutamate decarboxylase in cerebellum w as investigated by using gel electrophoresis and antisera that specifi cally recognize the individual isoforms of brain glutamate decarboxyla se (termed GAD(65) and GAD(67)). The antisera were prepared against pe ptides that corresponded to amino acid sequences specific to each isof orm. Each antiserum reacted specifically with the appropriate peptide in an ELISA and with the appropriate form of GAD on immunoblots. Nonde naturing gradient gel electrophoresis indicated that GAD is principall y multimeric with monomeric forms comprising <3% of the total. Immunop recipitation and immunoaffinity chromatography experiments were perfor med with antisera W624 and W883, which were prepared against peptides specific to GAD(65) and GAD(67), respectively. Immunoprecipitates prep ared from cerebellar supernatants with W624 contained both GAD(65) and GAD(67), whereas some GAD(67) was left in the supernatant. In a simil ar manner, immunoprecipitates prepared with W883 contained both GAD(65 ) and GAD(67), whereas some GAD(65) remained in the supernatant. In ad dition, immunoaffinity columns prepared with either W624 or W883 retai ned both GAD(65) and GAD(67) even after extensive washing. These resul ts are consistent with the presence of heteromultimers of GAD(65) and GAD(67) in cerebellum in addition to homomers of each form.