THE SYNTHESIS OF GLUTAMATE BY RAT BRAIN MITOCHONDRIA

Publisher Website
Google Scholar
Abstract
—: The synthesis of glutamate from 2‐oxoglutarate generated by the citric acid cycle and ammonium acetate has been studied in brain mitochondria of synaptic or non synaptic origin.Non synaptic brain mitochondria synthesise glutamate at twice the rate (1.3 nmol. min−1. mg protein−1) of synaptic mitochondria (0.65 nmol. min−1. mg protein−1) when pyruvate is the precursor for 2‐oxoglutarate, but at a similar rate (0.9 and 0.7 nmol. min−1, mg protein−1) when 3 hydroxybutyrate is the precursor.Glutamate synthesis from ammonium acetate and extramitochondrially addcd 2‐oxoglutarate (5 mM) by both synaptic and nonsynaptic mitochondria was 5‐fold higher (5‐6nmol. min−1. mg protein−1) than glutamate synthesis from endogenously produced 2‐oxoglutarate. In the uncoupled state (or un‐coupler + oligomycin) the rate was reduced by half. (2.5‐3 nmol. min−1. mg protein−1) as compared to mitochondria synthesising glutamate in states 3 or 4 (± oligomycin).The changes in brain mitochondrial nicotinamide nucleotide redox state have been monitored by fluorimetric, spectrophotometric and enzymatic techniques during glutamate synthesis and compared with liver mitochondria under similar conditions. On the instigation of glutamate synthesis by NH+4 addition a significant NAD(P)H oxidation occurs with liver mitochondria but no detectable change occurs with brain mitochondria.Leucine (2 mM) causes a doubling of glutamate synthesis by both synaptic and non synaptic brain mitochondria with no detectable change in the NAD(P)H redox state.The results are discussed with respect to the control of glutamate synthesis by mitochondrial redox potential and the possible intramitochondrial compartmentation of this process.