Fig. 4: Amino acid transporters and transaminases.

a, b Cells can either import amino acids from the extracellular environment or synthesize them inside the cell. Amino acid transporters are required to transfer them across the plasma membrane (shown in a), and transaminases are required to generate amino acids from sugar precursors and nitrogen from other amino acids (shown in b). Amino acid transporters and transaminases contribute to metabolic reprogramming in cancer through manipulation of the amino acid pool inside and outside cancer cells. Their impact on the tumor microenvironment is associated with tumor aggressiveness; some induce tumor cell growth and expansion through activation of signaling pathways (e.g., mTORC1 activation) or inactivation of tumor suppressors, while others result in apoptotic cell death. Amino acids are in green, and other metabolites are in red. Bright red represents transporters. Yellow boxes signify enzymes. The relative sizes of Lys and Arg represent the tendency to be transferred across CAT1 in a cancer setting. SLC6A14 solute carrier family 6 member 14, LAT1 large-neutral amino acid transporter 1, ASCT2 alanine, serine, cysteine-preferring transporter 2, xCT/CD98hc (4FC2) cystine/glutamate heterodimeric antiporter, CAT2B cationic amino acid transporter 2B, CAT1 cationic amino acid transporter 1, GLS glutaminase, GS glutamine synthetase, PSAT1 phosphoserine aminotransferase 1, AST aspartate aminotransferase, also known as glutamic oxaloacetic transaminase (GOT). GOT1 is in the cytosol and GOT2 in mitochondria, ASNS asparagine synthetase, ALT alanine aminotransferase, EAA essential amino acid, Na⁺, sodium ion, Cl⁻ chloride ion, Gln glutamine, Leu leucine, AA amino acid, Gly glycine, Glu glutamic acid, Cys cysteine, Cys cystine, Lys, lysine, NH₄⁺ ammonium ion, Asn asparagine, Ala alanine, Asp aspartic acid, Ser serine, PHP 3-phosphohydroxypyruvate, α-KG alpha-ketoglutarate, e⁻ electron, NADPH reduced nicotinamide adenine dinucleotide phosphate, NAD⁺ oxidized NADPH, OAA oxaloacetate.