Question: What molecule or ion capable of donating a hydron, is associated with Solute carrier family 10 member 4 and the promotion of acidification in mice?
Context: An acid is a molecule or ion capable of donating a hydron (proton or hydrogen ion H), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid). Solute carrier family 10 member 4 is a protein that in humans is encoded by the SLC10A4 gene.  In mice, it appears to promote acidification of synaptic vesicles containing monoamines, enhancing their uptake, and is co-expressed with VMAT2 and VAChT. Peptide transporter 1 (PepT 1) also known as solute carrier family 15 member 1 (SLC15A1) is a protein that in humans is encoded by "SLC15A1" gene.  PepT 1 is a solute carrier for oligopeptides.  It functions in renal oligopeptide reabsorption and in the intestines in a proton dependent way, hence acting like a cotransporter. Zinc transporter proteins, or simply zinc transporters, are membrane transport proteins of the solute carrier family which control the membrane transport of zinc and regulate its intracellular and cytoplasmic concentrations.  They include two major groups: (1) the zinc transporter (ZnT) or solute carrier 30 (SLC30) family, which controls the efflux of zinc from the cytoplasm out of the cell and from the cytoplasm into vesicles; and (2) the zinc importer, Zrt- and Irt-like protein (ZIP), or solute carrier 39A (SLC39A) family, which controls the influx of zinc into the cytoplasm from outside of the cell and from vesicles. Sodium/bile acid cotransporter also known as the Na-taurocholate cotransporting polypeptide (NTCP) or liver bile acid transporter (LBAT) is a protein that in humans is encoded by the "SLC10A1" (solute carrier family 10 member 1) gene. An organic cation transport protein mediates the transport of organic cations across the cell membrane.  These proteins are members of the solute carrier family, subfamily 22.  This family of proteins can also transport zwitterions and anions, though it is a different subfamily of solute carrier proteins than the organic anion transporters. An organic anion-transporting polypeptide (OATP) is a membrane transport protein or 'transporter' that mediates the transport of mainly organic anions across the cell membrane.  Therefore, OATPs are present in the lipid bilayer of the cell membrane, acting as the cell's gatekeepers.  OATPs belong to the Solute Carrier Family (SLC), more specifically the Solute Carrier Organic Anion (SLCO) gene subfamily The SLC10A2 (solute carrier family 10 member 2) gene in humans encodes the known as the apical sodium–bile acid transporter (ASBT) or as the ileal bile acid transporter (IBAT). Glucose transporter type 4 (GLUT-4), also known as solute carrier family 2, facilitated glucose transporter member 4, is a protein encoded, in humans, by the "SLC2A4" gene.  GLUT4 is the insulin-regulated glucose transporter found primarily in adipose tissues and striated muscle (skeletal and cardiac).  The first evidence for this distinct glucose transport protein was provided by David James in 1988.  The gene that encodes GLUT4 was cloned and mapped in 1989. Monocarboxylate transporter 10 (MCT 10), also known as aromatic amino acid transporter 1 and T-type amino acid transporter 1 (TAT1) and solute carrier family 16 member 10 (SLC16A10), is a protein that in humans is encoded by the "SLC16A10" gene.  SLC16A10 is a member of the solute carrier family.
Answer: An acid