Glutamate aspartate transporter

Palmieri, L., Pardo, B., del Arco, A. etal. Citrin and aralarl are Ca2+-stimulated aspartate/glutamate transporters in mitochondria. EMBO J. 20 5060-5069, 2001. 

Palmieri, L., Villa, A. et al (2003) Identification and metabolic role of the mitochondrial aspartate-glutamate transporter in Saccharomyces cerevisiae. 

A.3.7.6 Aspartate/Glutamate transporter AcaP L. lactis subsp lactis and subsp. cremoris Trip et al. 2013... 

FIGURE 31-7 Mitochondrial carriers. Ions and small molecules enter the intermembrane space, since the outer mitochondrial membrane is not a significant permeability barrier. However, the inner mitochondrial membrane is impermeable to ions except those for which there are specific carriers. Most of the carriers are reversible, as indicated by two-headed arrows. Compounds transported in one direction are indicated in red. The ATP/ADP translocase and the aspartate-glutamate carrier are both electrophoretic their transport is driven in the direction of the mitochondrial membrane potential, as indicated by red arrows. Glutamine is carried into the matrix by an electroneutral carrier. The unimpaired functioning of mitochondrial carriers is essential for normal metabolism. (Adapted with permission from reference [70].)... 

Although all five glutamate transporter subtypes support uncoupled chloride conductances, there are a number of distinct differences between the transporter subtypes. The current generated by EAAT4 and EAAT5 is predominantly owing to chloride ions, and in the case of L-aspartate transport by EAAT4, it has been estimated that up to 95%... 

The brain contains several transporters specialized for rapid uptake of neurotransmitters glutamate and aspartate,423-425 glycine,426 y-aminobutyrate (Gaba),427/428 and catecholamines and also for taurine, L-proline,429 serotonin,430 and other substances. Many of these are not only Na+ dependent but also require cotransport of Cl-.428-430 There are several different glutamate transporter genes with specialized distribution in the brain and other tissues.423 424... 

Citrin is an aspartate-glutamate antiporter that has a role both in the urea cycle and in the malate aspartate shuttle. It is necessary for the transport of aspartate produced in the mitochondria into the cytosol, where it is used by AS. Its role in the malate-aspartate shuttle is to transport cytosolic NADH reducing equivalents into the mitochondria, where they are used in oxidative phosphorylation. Defects in citrin cause citrullinemia type II. Patients manifest later-onset intermittent hyperammonemic encephalopathy as in HHH syndrome. 

The increase in glutamate favors transamination of oxaloacetate and limits oxaloacetate availability for phosphoenolpyruvate synthesis. When the [NADH]/[NAD+] ratio is low, malate formation occurs more readily. The cytosolic PEPCK is relatively unaffected by the mitochondrial [NADH]/[NAD+] ratio. Once malate and aspartate are transported to the cytosol and they are reconverted to oxaloacetate, cytosolic PEPCK can convert it to phosphoenolpyruvate. 

TTie actual meanings of the acronyms (GLAST, glutamate-aspartate transporter GLT. glutamate transporter EAAC. excitatory amino acid carrier EAAT. excitatory amino acid transporter) are not important, as they do not reflect functional differences among the transporters. 

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