Utilization of glutamate for phospho enolpyruvate and aspartate synthesis in kidney cortex mitochondria of rabbit

Abstract

1. 1. Utilization of glutamate for both phospho enolpyruvate and aspartate synthesis in kidney cortex mitochondria of the rabbit was studied under three metabolic conditions (state 3, uncoupled state and in the presence of uncoupler and oligomycin) in order to induce a high respiratory activity with an oxidized state of the nicotinamide dinucleotides but with varied intramitochondrial ATP levels. 2. 2. The highest rates of glutamate deamination and thus of phospho enolpyruvate formation were observed in uncoupled mitochondria incubated without oligomycin, i.e. under conditions of low intramitochondrial ATP content. Aspartate synthesis was high in both State 3 and the uncoupled state. 3. 3. In contrast to liver, addition of oligomycin to uncoupled kidney cortex mitochondria in order to increase the mitochondrial ATP/ADP ratio resulted in an inhibition of glutamate deamination, phospho enolpyruvate formation and aspartate synthesis. Atractyloside augmented an inhibitory effect of oligomycin. 4. 4. Addition of either ATP trapping system or ADP to mitochondria incubated in uncoupled-plus-oligomycin state resulted in the abolishing of the inhibition of both phospho enolpyruvate and aspartate synthesis, due to a depletion of intramitochondrial ATP content. 5. 5. In contrast to liver, leucine, which activates glutamate dehydrogenase, caused an acceleration of glutamate deamination in kidney cortex mitochondria, accompanied by an enhancement of phospho enolpyruvate formation. On the other hand, aspartate synthesis was not affected by leucine. 6. 6. In the uncoupled-plus-oligomycin state, leucine abolished an inhibitory effect of ATP and/or GTP on both glutamate deamination and phospho enolpyruvate synthesis. However, it did not relieve the inhibition of aspartate formation. 7. 7. In the presence of malate in addition to glutamate, oligomycin inhibited neither aspartate formation nor phospho enolpyruvate synthesis, since under these conditions an accumulation of energy did not occur in mitochondria due to an efficient phospho enolpyruvate formation. 8. 8. The data indicate that in contrast to liver, in kidney cortex mitochondria, utilizing glutamate as a substrate, the rates of both phospho enolpyruvate and aspartate synthesis depend greatly upon the mitochondrial energy level and the availability of both oxaloacetate and leucine. d