| Property | Summary |
|---|---|
| Gene name | **SLC25A13** (solute carrier family 25 member 13); also called **AGC2** (aspartate/glutamate carrier 2) (pqac-00000000, pqac-00000008) |
| Protein names / aliases | **Citrin**; **electrogenic aspartate/glutamate antiporter SLC25A13**; **mitochondrial aspartate-glutamate carrier 2 (AGC2)**; **ARALAR2** / **aralar-related gene 2** (pqac-00000001, pqac-00000008) |
| UniProt ID | **Q9UJS0** (user-provided UniProt identity; matched in literature to human SLC25A13/citrin/AGC2) (pqac-00000001, pqac-00000015) |
| Organism | **Homo sapiens (human)** (user-provided identity; disease and biochemical literature consistently describe human SLC25A13/citrin deficiency) (pqac-00000015, pqac-00000017) |
| Protein family | Member of the **SLC25 mitochondrial carrier family**; specifically an **aspartate/glutamate carrier** of the inner mitochondrial membrane (pqac-00000004, pqac-00000023) |
| Subcellular localization | Localized to the **inner mitochondrial membrane**; participates in metabolite exchange between mitochondrial matrix and cytosol/intermembrane-space-facing side (pqac-00000003, pqac-00000007) |
| Primary tissue expression | Highest functional importance in **liver/hepatocytes**, where it is the predominant or sole AGC isoform; also expressed in **intestinal epithelium/small intestine**; lower or restricted expression in **kidney** and **heart**, and low brain expression limited to select neuronal clusters (pqac-00000005, pqac-00000013, pqac-00000038) |
| Transport substrates | **Exports aspartate** from the mitochondrial matrix in exchange for **import of glutamate plus H+** into mitochondria (pqac-00000000, pqac-00000001, pqac-00000013) |
| Transport mechanism | **Electrogenic aspartate/glutamate antiport** operating by an **alternating-access** mechanism with matrix-open and cytoplasmic-open states, controlled by conserved salt-bridge gate networks; proton-coupled glutamate import helps drive net flux in the malate-aspartate shuttle (pqac-00000002, pqac-00000004, pqac-00000026) |
| Key metabolic pathways | Core component of the **malate-aspartate shuttle** for cytosolic NADH reoxidation and mitochondrial NADH generation; supplies cytosolic aspartate for the **urea cycle**; supports **gluconeogenesis** via oxaloacetate/aspartate coupling; also supports **protein**, **purine**, and **pyrimidine** synthesis and broader hepatic redox/energy metabolism (pqac-00000008, pqac-00000010, pqac-00000012) |
| Associated diseases | Biallelic pathogenic variants cause **citrin deficiency (CD)** with age-dependent phenotypes: **NICCD** (neonatal intrahepatic cholestasis caused by citrin deficiency), **FTTDCD** (failure to thrive and dyslipidemia caused by citrin deficiency), and **CTLN2/AACD** (adult-onset type II citrullinemia / adolescent-adult citrin deficiency); complications include **hyperammonemia**, **fatty liver**, **pancreatitis**, **cirrhosis**, and risk of **hepatocellular carcinoma** (pqac-00000015, pqac-00000016, pqac-00000021) |
| Key structural features | Unusual **three-domain** mitochondrial carrier with an **N-terminal EF-hand domain**, a **canonical carrier domain** of three repeated modules/six transmembrane helices, and a **C-terminal amphipathic helix**; forms **homodimers**; recent work indicates **only EF-hand 2 binds Ca2+** and that **Ca2+ binding is not required for transport regulation**, contrary to older models (pqac-00000023, pqac-00000025, pqac-00000027) |


*Table: This table summarizes the key molecular, cellular, metabolic, and disease-related properties of human SLC25A13/citrin. It is useful as a quick reference linking transporter function and structure to citrin deficiency phenotypes.*