Relationship between the 4-aminobutyrate bypath and the oxidation of 2-oxoglutarate in rat brain mitochondria.

— A method is described to evaluate simultaneously the contributions of 2-oxoglutarate oxidation and the GABA bypath to succinate production in isolated rat brain mitochondria. 2-Oxoglutarate oxidation is under respiratory control whereas the activity of the GABA shunt is but slightly affected by the mitochondrial energy state. The oxidation of GABA is half-maximal with 5mm-GABA. GABA does not affect 2-oxoglutarate oxidation. 1 mm-2-oxoglutarate is optimal for GABA oxidation, whereas higher concentrations inhibit the shunt activity. The rate of GABA oxidation observed in vitro (5 nmol/min.mg mitochondrial protein) is comparable to the activity of the shunt under in viuo conditions. The control and the compartmentation of GABA oxidation are discussed.