transamination

Transamination is a biochemical process in which an amino group is transferred from an amino acid to a keto acid, producing a new amino acid and a new keto acid. Most transaminations are catalyzed by aminotransferases (transaminases) and are reversible, allowing organisms to interconvert amino acids and to redistribute nitrogen during metabolism. The donor is typically an α-amino acid such as glutamate, and the common acceptor is α-ketoglutarate, linking amino acid metabolism to the citric acid cycle. The reaction requires pyridoxal phosphate (PLP), the active form of vitamin B6, which serves as a prosthetic group and cofactor in the transfer of amino groups.

Two well-characterized enzymes in humans are alanine aminotransferase (ALT) and aspartate aminotransferase (AST). ALT catalyzes the transfer of the amino group from alanine to α-ketoglutarate, yielding pyruvate and glutamate. AST catalyzes the transfer from aspartate to α-ketoglutarate, yielding oxaloacetate and glutamate. These reactions are routinely used to channel nitrogen into central metabolism and to generate substrates for energy production and biosynthesis. Closely related transaminases are present in many tissues and in plants and microbes, supporting de novo synthesis of nonessential amino acids.

Biological significance: Transamination participates in amino acid biosynthesis, catabolism, and nitrogen balance. It provides a mechanistic framework for the interconversion of amino acids and for the assimilation of amino groups into central carbon metabolism. In clinical settings, measurement of ALT and AST activities in blood serves as a diagnostic tool for liver and heart tissue injury, though interpretation requires context and may involve other enzymes and markers.