Transport of glutamate and aspartate across the membranes of rat liver mitochondria

Chromatographic analyses have indicated that aspartate and glutamate constitute from 50–70% of the total free amino acids in freshly isolated mitochondria. Radioactive tracer studies indicate that while the l-isomers of glutamate and aspartate are rapidly accumulated by mitochondria, the d-isomers of these amino acids do not penetrate the mitochondrial membrane. The action of two inhibitory compounds, 1-fluoro-2,4-dinitrobenzene (Sanger's reagent) and tannic acid, on the transport of l-glutamate and l-aspartate has been examined. A marked inhibition of l-glutamate transfer by 1-fluoro-2,4-dinitrobenzene is observed. A corresponding effect on the transport of either l-aspartate or the anionic substrate, succinate has not been found. Tannic acid, an agent previously known to inhibit certain carrier-mediated solute fluxes in mitochondria, is shown also to inhibit the uptake of both l-glutamate and l-aspartate. These findings are consistent with the view that the mitochondrial membranes of rat liver cells contain distinct, stereospecific transport mechanisms for aspartate and glutamate.