Binding of [3H]gamma-vinyl-GABA to GABA-transaminase in brain homogenates

[3H]Gamma-vinyl-GABA, an irreversible inhibitor of GABA-transaminase, was used to label the enzyme in homogenates of rat brain. The binding procedure utilized was found to be specific for GABA-transaminase and linear with tissue obtained from several regions of rat brain up to concentrations of 8 micrograms protein/microliter. The specific binding was directly proportional to the activity of the enzyme measured in vitro and was completely inhibited by the GABA-transaminase inhibitors aminooxyacetic acid (100 microM) and 3-mercaptopropionic acid (1.0mM). The binding procedure was used to estimate the amount of active enzyme present in a homogenate of striatal tissue.