Control of ammoniagenesis by alpha-ketoglutarate in rat kidney mitochondria

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Abstract
To better understand the control of renal ammoniagenesis, measurements of ammonia formation by isolated rat kidney mitochondria were made at different pH values with glutamine and .alpha.-ketoglutarate as substrates. In the absence of .alpha.-ketoglutarate, ammonia formation from glutamine was lower at pH 6.8 than 7.4; the opposite was true when .alpha.-ketoglutarate was added to the medium. In the presence of .alpha.-ketoglutarate, product analysis showed that the increase in ammonia formation at pH 6.8 was due to increased net flux through glutamate dehydrogenase. The increase was abolished in the presence of sodium arsenite, suggesting a role for augmented .alpha.-ketoglutarate metabolism at acid pH. Acid pH was shown to increase .alpha.-ketoglutarate oxidation by mitochondria, to stimulate the disapperance of .alpha.-ketoglutarate from the extramitochondrial medium, and to augment .alpha.-ketoglutarate dehydrogenase flux. The augmented flux occurring at acid pH when mitochondria were incubated with glutamine plus .alpha.-ketoglutarate was associated with an increase in the pH gradient across the inner mitochondrial membrane, an increase in the matrix glutamate concentration, and a decrease in the matrix .alpha.-ketoglutarate and ammonia concentrations, but no change in pyridine nucleotides. The increased glutamate dehydrogenase flux maybe the result of increased glutamate deamination rather than decreased amination of .alpha.-ketoglutarate. H+ accelerates .alpha.-ketoglutarate dehydrogenase flux in isolated rat kidney mitochondria. This increase in flux may alter .DELTA.pH and matrix metabolite levels, thereby stimulating glutamate deamination and enhancing renal ammoniagenesis.