transaminations

Transaminations are biochemical reactions in which an amino group is transferred from a donor amino acid to an acceptor α-keto acid, producing a new amino acid and a new α-keto acid. They are central to amino acid metabolism and nitrogen transport in many organisms, enabling interconversion among amino acids and connecting amino acid metabolism with carbohydrate metabolism.

Most transaminations are catalyzed by pyridoxal phosphate (PLP)–dependent enzymes, often called aminotransferases. The reaction typically proceeds by a ping-pong Bi-Bi mechanism: the amino group from the donor forms an external aldimine with PLP, generating a pyridoxamine phosphate intermediate; the amino group is then transferred to the acceptor α-keto acid, yielding a new amino acid and a PLP-bound keto intermediate, which regenerates PLP and releases the product. The overall process is usually reversible.

Common donor amino acids include glutamate and alanine, and common acceptors include pyruvate and oxaloacetate, forming alanine from pyruvate, aspartate from oxaloacetate, and glutamate from α-ketoglutarate, among others. Through these exchanges, transaminations link amino acid metabolism with the central carbon metabolism and play a key role in nitrogen balance and gluconeogenesis, particularly in liver and muscle tissue.

Clinical relevance is notable: aminotransferases such as alanine transaminase (ALT) and aspartate transaminase (AST) are widely used as biomarkers of liver injury; elevations indicate hepatocellular damage, with the AST/ALT ratio aiding certain differential diagnoses, including alcoholic liver disease. Transaminases also function in plants and microorganisms, where they participate in the biosynthesis and degradation of amino acids.