TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
*2.A.22.1.1









Serotonin (5-hydroxytryptamine; 5 HT):Na+:Cl- symporter, SERT.A  Also transports amphetamines; blocked by cocaine and tricyclic antidepressants such as Prozac; interacts directly with the secretory carrier-associated membrane protein-2 (SCAMP2; O15127) to regulate the subcellular distribution (Muller et al., 2006). Uses an alternating sites mechanism with all 3 substrates bound (Zhang and Rudnick, 2006).  Molecular determinants for antidepressants in the human serotonin and norepinephrine  transporters have been identified (Andersen et al., 2011). A conserved asparagine residue in transmembrane segment 1 (TMS1) of the serotonin transporter dictates chloride-coupled neurotransmitter transport (Henry et al., 2011). The formation and breakage of ionic interactions with amino acids in transmembrane helices 6 and 8 and intracellular loop 1 may be of importance for substrate translocation (Gabrielsen et al., 2012). Methylation of the SLC6A4 gene promoter controls depression in men by an epigenetic mechanism (Devlin et al., 2010).  The 5HT Km is 0.4 micromolar (Banovic et al. 2010).  Regulated allosterically by ATM7 which stabilizes the outward-facing conformation of SERT (Kortagere et al. 2013).  Functional and regulatory mechanisms involving the N- and C-terminal hydrophilic domains have been considered (Fenollar-Ferrer et al. 2014).  The range of substrates bound and transported has been predicted (Kaufmann et al. 2009).  TMS3 may function in substrate and antagonist recognition (Walline et al. 2008).  The 3-d x-ray structure with antidepressants bound have been solved, leading to mechanistic predictions; antidepressants lock SERT in an outward- open conformation by lodging in the central binding site, located between transmembrane helices 1, 3, 6, 8 and 10, directly blocking serotonin binding (Coleman et al. 2016).  Na+ and cocaine stabilize outward-open conformations of SERT and decrease phosphorylation while agents that stabilize inward-open conformations (e.g., 5-HT, ibogaine) increase phosphorylation. The opposing effects of the inhibitors, cocaine and ibogaine, were each reversed by an excess of the other inhibitor. Inhibition of phosphorylation by Na+ and stimulation by ibogaine occurred at concentrations that induced outward opening and inward opening, respectively (Zhang et al. 2016).  SERT is regulated by multiple molecular mechanisms including its physical interaction with intracellular proteins including the ASCT2 (alanine-serine-cysteine-threonine 2; TC# 2.A.23.3.2), co-expressed with SERT in serotonergic neurons and involved in the transport of small neutral amino acids across the plasma membrane (Seyer et al. 2016).  Transports substituted amphetamine, 3,4-methylenedioxy-methamphetamine (MDMA, ecstasy) (Sealover et al. 2016).  A naturally occurring mutation, I425V, associated with obsessive-compulsive disorder and other neuropsychiatric disorders, activates hSERT and eliminates stimulation via the cyclicGMP-dependent pathway (Zhang et al. 2007).  The substituted amphetamine, 3,4-methylenedioxy-methamphetamine (MDMA, ecstasy), is a widely used drug of abuse that induces non-exocytotic release of serotonin, dopamine, and norepinephrine through their cognate transporters as well as blocking the reuptake of neurotransmitter by the same transporters. In this transporter, Glu394 plays a role in MDMA recognition (Sealover et al. 2016). Intestinal dysbiosis may upregulate SERT expression and contribute to the development of chronic constipation (Cao et al. 2017).

Eukaryota
Metazoa
SERT or SLC6A4 of Homo sapiens
*2.A.22.1.2









Noradrenaline:Na+ symporter (NET) (also transports 1-methyl-4-tetrahydropyridinium and amphetamines; it is a target of cocaine and amphetamines as well as of therapetics for depression, obsessive-compulsive disorders, and post-traumatic stress disorder. This homooligomeric transporter binds one substrate molecule per transporter subunit (Schwartz et al., 2005; Schlessinger et al., 2011; Andersen et al., 2011). Extracellular loop 3 contributes to substrate and inhibitor selectivity (Lynagh et al. 2013). The highly conserved MELAL and GQXXRXG motifs, located in the second transmembrane domain and the first intracellular loop of hNET, respectively, are determinants of NET cell surface expression, and substrate and inhibitor binding (Sucic and Bryan-Lluka 2007).

Eukaryota
Metazoa
SLC6A2 of Homo sapiens
*2.A.22.1.3









Dopamine:Na+ symporter, DAT (also takes up amphetamines in symport with Na+ which promotes intracellular Na+-dependent dopamine efflux (Khoshbouei et al., 2003)) [Inhibited by cocaine, amphetamines, neurotoxins, antidepressants and ethanol (Chen et al., 2004)]. (Zn2+ potentiates uncoupled Cl- conductance (Meinild et al., 2004)).  A conserved salt bridge between TMSs 1 and 10 constitutes an extracellular gate (Pedersen et al. 2014).  DAT is regulated by D3 dopamine receptors (Zapata et al., 2007). P25α (tubulin polymerization-promoting protein, TPPP; 094811) increases dopamine transporter localization to the plasma membrane (Fjorback et al., 2011). Mediates paraquat (an herbicide) neurotoxicity (Rappold et al., 2011).  Membrane cholesterol modulates the outward facing conformation and alters cocaine binding (Hong and Amara 2010).  Threonine 53 phosphorylation in the rat orthologue (P23977) (Serine 53 in the human transporter) regulates substrate reuptake and amphetamine-stimulated efflux (Foster et al. 2012).  DAT is enriched in filopodia and induces filopodia formation (Caltagarone et al. 2015).  Dasotraline is a novel inhibitor of dopamine and norepinephrine reuptake used for the treatment of attention-deficit/hyperactivity disorder (ADHD) (Hopkins et al. 2015). When in complex with 1-(1-benzofuran-5-yl)-N-methylpropan-2-amine (5-MAPB), a psychoactive adictive agonists, DAT can exhibit conformational transitions that spontaneously isomerize the transporter into inward-facing state, similarly to that observed in dopamine-bound DAT (Sahai et al. 2016).  The cytoplasmic N- and C-terminal domains contribute to substrate and inhibitor binding (Sweeney et al. 2016). DAT can exist as a monomer or a cooperative dimer subject to allosteric regulation (Cheng et al. 2017). Cocaine binds in the S1 site to stabilize an inactive form of DAT (Krout et al. 2017). Dopamine efflux is caused by 3,4-methylenedioxypyrovalerone (MDPV) (Shekar et al. 2017).

Eukaryota
Metazoa
SLC6A3 of Homo sapiens
*2.A.22.1.4









Antidepressant- and cocaine-sensitive dopamine transporter, T23G5.5 (Km for dopamine, 1.2 µM; dependent on extracellular Na+ and Cl-; blocked by cocaine and D-amphetamine) (Jayanthi et al. 1998) (interacts with syntaxin 1A to regulate channel activity and dopaminergic synaptic transmission; Carvelli et al., 2008)
Eukaryota
Metazoa
T23G5.5 of Caenorhabditis elegans (Q03614)
*2.A.22.1.5









High affinity octopamine transporter, OAT (also transports tyramine and dopamine in the 0.4-3.0 μM range (Donly et al., 2007)).
Eukaryota
Metazoa
OAT of Trichoplusia ni (Q95VZ4)
*2.A.22.1.6









The dopamine/norepinephrine transporter (SmDAT) (Larsen et al. 2011).

Eukaryota
Metazoa
DAT of Schistosoma mansoni (E9LD23)
*2.A.22.1.7









Dopamine transporter.  The 3-d structure is known to 3.0 Å resolution (Penmatsa et al. 2013).  The crystal structure, bound to the tricyclic antidepressant nortriptyline, shows the transporter locked in an outward-open conformation with nortriptyline wedged between transmembrane helices 1, 3, 6 and 8, blocking the transporter from binding substrate and from isomerizing to an inward-facing conformation. Although the overall structure is similar to that of its prokaryotic relative LeuT, there are multiple distinctions, including a kink in transmembrane helix 12 halfway across the membrane bilayer, a latch-like carboxy-terminal helix that caps the cytoplasmic gate, and a cholesterol molecule wedged within a groove formed by transmembrane helices 1a, 5 and 7.

Eukaryota
Metazoa
Dopamine transporter of Drosophila melanogaster
*2.A.22.1.8









Snf-10 transporter.  Required for protease-mediated activation of sperm motility.  Present in the plasma membrane before activation, but assumes a polarized localization to the cell body region that is dependent on membrane fusions mediated by the dysferlin FER-1 (Fenker et al. 2014).

Eukaryota
Metazoa
Snf-10 of Caenorabditis elegans
*2.A.22.1.9









The sodium-dependent serotonin transporter of 622 aas and 12 TMSs, SerT.  Terminates the action of serotonin by its high affinity reuptake into presynaptic terminals (Demchyshyn et al. 1994). Substrates have been predicted based on modeling studies (Kaufmann et al. 2009).

Eukaryota
Metazoa
SerT of Drosophila melanogaster (Fruit fly)
*2.A.22.1.10









Serotonin transporter, Mod-5, of 671 aas and 12 TMSs.  Functions in thermotaxis memory behavior (Li et al. 2013).

Eukaryota
Metazoa
Mod-5 of Caenorhabditis elegans
*2.A.22.2.1









Proline:Na+ symporter
Eukaryota
Metazoa
Proline transporter of Rattus norvegicus
*2.A.22.2.2









Glycine:Na+ symporter, GlyT1c (glycine/2Na+/1Cl- symporter)
Eukaryota
Metazoa
Glycine transporter (GlyT1c) of Rattus norvegicus
*2.A.22.2.3









Neutral and cationic amino acid:Na+:Cl- symporter, B0+. The rat homologue (NP_001032633) transports basic and zwitterionic amino acids, but not proline, aspartic acid and glutamic acid (Uchiyama et al, 2008).

Eukaryota
Metazoa
SLC6A14 of Homo sapiens
*2.A.22.2.4









Gut epithelium absorptive neutral amino acid Na+- or K+-dependent transporter, CAATCH1 (electrogenic; Cl--independent. Substrates: L-proline-preferring + Na+; L-threonine-preferring + K+; also transports L-methionine) (CAATCH1 can also function as an amino acid-gated cation [Na+ and K+] channel.)

Eukaryota
Metazoa
Neutral amino acid transporter CAATCH1 of Manduca sexta
*2.A.22.2.5









Gut epithelium absorptive neutral amino acid, K+- and Na+-dependent transporter KAAT1 (electrogenic; Cl--dependent; activated by alkaline pH; all zwiterionic amino acids except methyl AIB are substrates). CAATCH1 is 95% identical to KAAT1. Leu > Thr and Pro.
Eukaryota
Metazoa
Neutral amino acid transporter KAAT1 of Manduca sexta
*2.A.22.2.6









Glycine:Na+ transporter, GlyT2b (glycine/3Na+/1Cl- symporter, SLC6A5). GlyT2 and VIAAT cooperate to determine the vesicular glycinergic phenotype (Aubrey et al., 2007). Startle disease in Irish wolfhounds is associated with a microdeletion in the glycine transporter GlyT2 gene (Gill et al., 2011). A dominant hyperekplexia (startle disease) mutation Y705C in humans alters trafficking and the biochemical properties of GlyT2 (Gimenez et al. 2012).

Eukaryota
Metazoa
Glycine transporter (GlyT2b) of Mus musculus
*2.A.22.2.7









Acetylcholine/choline:Na+ symporter, Snf-6 (interacts with dystrophin which determines its localization to the neuromuscular junction) (Kim et al., 2004)

Eukaryota
Metazoa
Snf-6 of Caenorhabditis elegans (O76689)
*2.A.22.2.8









Cation-dependent nutrient amino acid transporter, AAT1 (L-phe > cys > his > ala > ser > met > ile > tyr > D-phe > thr > gly) (Bondko et al., 2005)
Eukaryota
Metazoa
AAT1 of Aedes aegypti (Q6VS78)
*2.A.22.2.9









The Densovirus type-2 (BmDNV-2) receptor; putative amino acid transporter (625aas;11-12TMSs)

Eukaryota
Metazoa
Nsd-2 of Bombyx mori (B2ZXL8)
*2.A.22.2.10









Sodium- and chloride-dependent glycine transporter 2 (GlyT-2) (GlyT2) (Solute carrier family 6 member 5).  The STAS domain has been solved by x-ray crystalography (PDB# 3LLO).  Functions to remove and recycle synaptic glycine from inhibitory synapses.  Mutations in GlyT are a common cause of hyperakplexia or startle disease in humans. The ER chaparone, calnexin, facilitates GlyT processing (Arribas-González et al. 2013).

Eukaryota
Metazoa
SLC6A5 of Homo sapiens
*2.A.22.2.11









Sodium-dependent proline transporter (Solute carrier family 6 member 7)
Eukaryota
Metazoa
SLC6A7 of Homo sapiens
*2.A.22.2.12









Sodium- and chloride-dependent glycine transporter 1 (GlyT-1) (GlyT1) (Solute carrier family 6 member 9)
Eukaryota
Metazoa
SLC6A9 of Homo sapiens
*2.A.22.2.13









Sodium-dependent nutrient amino acid transporter 1 (DmNAAT1)

Eukaryota
Metazoa
NAAT1 of Drosophila melanogaster
*2.A.22.3.1









Betaine/GABA:Na+ symporter, BGT1. (Substrates include: betaine, GABA, diaminobutyrate, β-alanine, proline, quinidine, dimethylglycine, glycine, and sarcosine with decreasing affinity in that order).  Selective inhibitors have been identified (Kragholm et al. 2013).

Eukaryota
Metazoa
SLC6A12 of Homo sapiens
*2.A.22.3.2









γ-aminobutyric acid (GABA):Na+:Cl- symporter, GAT-1 (Stoichiometry, GABA:Na+ = 1:2 where both Na+ binding sites, Na1 and Na2, have been identified. Na2 but not Na1 can accommodate Li+ (Zhou et al., 2006)). Glutamine 291 is essential for Cl- binding (Ben-Yona et al., 2011). Four human isoforms have been identified, GAT-1, GAT-2, GAT-3, and GAT-4, all about 70% identical to each other (Borden et al., 1992). GAT-2 transports γ-aminobutyric acid and β-alanine (Christiansen et al, 2007) It also concentratively takes up β-alanine and α-fluoro-β-alanine (Liu et al., 1999). GAT1 is capable of intracellular Na+-, Cl-- and GABA-induced outward currents (reverse GABA transport; GABA efflux) (Bertram et al., 2011). An acidic amino acid residue in transmembrane helix 10 conserved in the Neurotransmitter:Sodium:Symporters is essential for the formation of the extracellular gate of GAT-1 (Ben-Yona and Kanner, 2012). It is required for stringent gating and tight coupling of ion- and substrate-fluxes in the GABA transporter family (Dayan et al. 2017). GAT-1 is the target of the antiepileptic drug, tiagabine (Kardos et al. 2010). The monomeric protein has been purified fused to GFP (Hu et al. 2017).

Eukaryota
Metazoa
SLC6A1 of Homo sapiens
*2.A.22.3.3









The taurine:Na+ symporter, TauT or SLC6A6 (also transports β-alanine and γ-aminobutyric acid (GABA); Tomi et al., 2008; Anderson et al., 2009).

Eukaryota
Metazoa
SLC6A6 of Homo sapiens
*2.A.22.3.4









Creatine:Na+ symporter
Eukaryota
Metazoa
Creatine transporter of Oryctolagus cuniculus
*2.A.22.3.5









Renal apical membrane creatine:Na2+:Cl- symporter (CRT) (Garcia-Delgado et al., 2007)
Eukaryota
Metazoa
CRT of Rattus norvegicus (P28570)
*2.A.22.3.6









γ-aminobutyric acid (GABA):Na+:Cl- symporter GAT-1 (stoichiometry = 1:2:1) (Jiang et al., 2005)
Eukaryota
Metazoa
GAT-1 of Caenorhabditis elegans (AAT02634)
*2.A.22.3.7









The GABA transporter, GAT4 (single mutations render this transporter C1- independent) (Zomot et al., 2007)
Eukaryota
Metazoa
GABA transporter GAT4 of Mus musculus (Q8BWA7)
*2.A.22.3.8









Mouse GABA, β-alanine, fluoro-β-alanine and taurine transporter-3 (GAT3) (Liu et al. 1999). Orthologous to rat and human GAT2; 72% identical to GAT4 (2.A.22.3.7) (takes up GABA with high affinity into presynaptic terminals). Also takes up the carnitine precursor, gamma-butyrobetaine (Nakanishi et al., 2011).

Eukaryota
Metazoa
GAT3 of Mus musculus (P31649)
*2.A.22.3.9









Sodium- and chloride-dependent GABA transporter 3 (GAT-3) (Solute carrier family 6 member 11)
Eukaryota
Metazoa
SLC6A11 of Homo sapiens
*2.A.22.3.10









Sodium- and chloride-dependent GABA transporter 2 (GAT-2) (Solute carrier family 6 member 13)
Eukaryota
Metazoa
SLC6A13 of Homo sapiens
*2.A.22.3.11









Sodium- and chloride-dependent creatine transporter 1 (CT1) (Creatine transporter 1) (Solute carrier family 6 member 8)
Eukaryota
Metazoa
SLC6A8 of Homo sapiens
*2.A.22.3.12









Sodium- and chloride-dependent GABA transporter, Ine (Protein inebriated) (Protein receptor oscillation A)

Eukaryota
Metazoa
Ine of Drosophila melanogaster
*2.A.22.4.1









High affinity tryptophan:Na+ symporter, TnaT (Androutsellis-Theotokis et al., 2003)
Bacteria
Firmicutes
TnaT of Symbiobacterium thermophilum
*2.A.22.4.2









The amino acid (leucine):2 Na+ symporter, LeuTAa (Yamashita et al., 2005). LeuT possesses two ion binding sites, NA1 and NA2, both highly specific for Na+ but with differing mechanisms of binding (Noskov and Roux, 2008). X-ray structures have been determined for LeuT in substrate-free outward-open and apo inward-open states (Krishnamurthy and Gouaux, 2012).  Extracytoplasmic substrate binding at an allosteric site controls activity (Zhao et al. 2011).  It has been proposed that the 5 TMS repeat derived from a DedA domain (9.B.27; Khafizov et al. 2010).  Mechanistic aspect of Na+ binding have been studied (Perez and Ziegler 2013).  Structural studies of mutant LeuT proteins suggest how antidepressants bind to biogenic amine transporters (Wang et al. 2013).  The detailed mechanism was studied by Zhao and Noskov, 2013.  Uptake involves movement of the substrate amino acid from the outward facing binding site, S1, to the inward facing binding site, S2, coupled with confrmational changes in the protein (Cheng and Bahar 2013).  The complete substrate translocation pathway has been proposed (Cheng and Bahar 2014). The inward facing conformation of LeuT has been solved (Grouleff et al. 2015).  Substrate-induced unlocking of the inner gatemay determinethe catalytic efficiency of the transporter (Billesbølle et al. 2015). Of the two Na+ binding sites, occupation of Na2 stabilizes outward-facing conformations presumably through a direct interaction between Na+ and transmembrane helices 1 and 8 whereas Na+ binding at Na1 influences conformational change through a network of intermediary interactions (Tavoulari et al. 2015). TMS1A movements revealed a substantially different inward-open conformation in lipid bilayer from that inferred from the crystal structure, especiallly with respect to the inner vestibule (Sohail et al. 2016).

Bacteria
Aquificae
LeuTAa of Aquifex aeolicus (2A65_A)
*2.A.22.4.3









The methionine/alanine uptake porter, MetPS (Trotschel et al., 2008) (MetP is the transporter; MetS is an essential auxiliary subunit).
Bacteria
Actinobacteria
MetPS of Corynebacterium glutamicum
MetP (563aas; Q8NRL8)
MetS (60aas; Q8NRL9)
*2.A.22.5.1









Hypothetical Na+-dependent permease
Archaea
Euryarchaeota
MJ1319 of Methanococcus jannaschii
*2.A.22.5.2









The 11 TMS Na+-dependent tyrosine transporter, Tyt1 (Quick et al., 2006)
Bacteria
Fusobacteria
Tyt1 of Fusobacterium nucleatum (Q8RHM5)
*2.A.22.5.3









Neurotransmitter:sodium symporter of 455 aas, MhsT.  The x-ray structures of two occluded inward-facing states with bound Na+ ions and L-tryptophan have been solved (4US4; Malinauskaite et al. 2014).  These structures provide insight into the cytoplasmic release of Na+. The switch from outward- to inward-oriented states is centered on the partial unwinding of transmembrane helix 5, facilitated by a conserved GlyX9Pro motif that opens an intracellular pathway for water to access the Na+2 site. Solvation through this TMS 5 pathway may facilitate Na+ release from the Na+2 site to the inward-open state (Malinauskaite et al. 2014). TMS5 plays a role in the binding and release of Na+ from the Na+2 site and in mediating conformational changes (Stolzenberg et al. 2017).

Bacteria
Firmicutes
MhsT of Bacillus halodurans
*2.A.22.5.4









Uncharacterized protein of 427 aas and 12 TMSs.

Archaea
Euryarchaeota
UP of Thermococcus profundus
*2.A.22.6.1









Na+/Amino acid transporter 1, SIT1/IMINO (SLC6A20). Transports imino acids such as proline (Km=0.2 mM), pipecolate, and N-methylated amino acids such as MeAIB and sarcosine (Na+-dependent, Cl--stimulated, pH-independent, voltage-dependent) (Li+, but not H+ can substitute for Na+) (Takanaga et al., 2005). It is a 2Na+/1Cl--proline cotransporter (Bröer et al., 2009).

Eukaryota
Metazoa
SIT1 of Rattus norvegicus (Q64093)
*2.A.22.6.2









Synaptic vesicle neutral amino acid:Na+ symporter NTT4/XT1/BOAT3 (SLC6A17) (catalyzes uptake of neurotransmitters into presynaptic vesicles (Zaia and Reimer, 2009).

Eukaryota
Metazoa
NTT4 of Rattus norvegicus (P31662)
*2.A.22.6.3









Kidney and intestinal apical membrane epithelial transporter for Na+-dependent, Cl--independent reabsorption of neutral amino acids. Many neutral L-amino acids bind with ~0.5 mM affinities Leu is the preferred substrate, but all large neutral non-aromatic L-amino acids bind to this transporter. Uptake of leucine is sodium-dependent. In contrast to other members of the neurotransmitter transporter family, this one does not appear to be chloride-dependent.  Activity is enhanced by collectrin (Tmem27), a collecting duct transmembrane (1 TMS) glycoprotein (Q9HBJ8) (Danilczyk et al., 2006). The Hartnup Disorder protein (mouse orthologue, (Q9D687) (Broer et al., 2004; 2008) forms a complex with collectrin and the brush border carboxypeptidase angiotensin-converting enzyme 2 (ACE2). Mutation as in Hartnup disorder (B0AT1(R240Q)) decreases complex formation and leads to neutral aminoaciduria and in some cases pellagra-like symptoms (Kowalczuk et al., 2008; Singer et al. 2012).  Collectrin is expressed in the simple embryonic kidney of amphibians such as Xenopus, the pronephros, at high levels (McCoy et al. 2008).           

Eukaryota
Metazoa
SLC6A19 of Homo sapiens
*2.A.22.6.4









The neutral amino acid transporter, B0AT3 (Slc6a18); XT2 (55% identical to 2.A.22.6.3)

Eukaryota
Metazoa
SLC6A18 of Homo sapiens
*2.A.22.6.5









solute carrier family 6, member 16
Eukaryota
Metazoa
SLC6A16 of Homo sapiens
*2.A.22.6.6









Sodium-dependent vesicular neutral amino acid transporter SLC6A17 (Sodium-dependent neurotransmitter transporter NTT4/BOAT3) (Solute carrier family 6 member 17) (Hägglund et al. 2013).

Eukaryota
Metazoa
SLC6A17 of Homo sapiens
*2.A.22.6.7









Sodium-dependent neutral amino acid transporter B(0)AT2 (Sodium- and chloride-dependent neurotransmitter transporter NTT73) (Sodium-coupled branched-chain amino-acid transporter 1) (Solute carrier family 6 member 15) (Transporter v7-3).  It is mainly expressed in neurons and plays a role in depression and stress vulnerability (Santarelli et al. 2015).

Eukaryota
Metazoa
SLC6A15 of Homo sapiens
*2.A.22.6.8









Sodium- and chloride-dependent transporter XTRP3 (Sodium/amino-acid transporter 1) (Solute carrier family 6 member 20) (Transporter rB21A homologue)

Eukaryota
Metazoa
SLC6A20 of Homo sapiens
*2.A.22.6.9









Sea bass amino acid uptake porter, SLC6A19 or B0AT1 of 634 aas.  Levels depend on diet (Rimoldi et al. 2015).

Eukaryota
Metazoa
SLC6A19 of Dicentrarchus labrax (European seabass) (Morone labrax)