Transaminases (Aminotransferases)

Transaminase is a name for a category of enzymes involved in exchange of an oxygen from an -keto acid (such as -ketoglutarate) and an amine from an amino acid (see here). Aminotransferases utilize a coenzyme, pyridoxal phosphate, that is derived from vitamin B 6. The functional part of the cofactor is an aldehyde functional group, -CHO, attached to a pyridine ring. Catalysis begins with condensation of this aldehyde with the amino group of an amino acid, to give a Schiff base, or aldimine, intermediate, followed by formation of a resonance-stabilized carbanion with a quinonoid structure, as shown in Figure 20.15. Depending on the bond labilized, formation of the aldimine can lead to a transamination, to decarboxylation, to racemization, or to numerous side chain modifications, such as -elimination.

Example transamination reactions are as follows:

> Alanine + -Ketoglutarate <-> Pyruvate + Glutamate

> Oxaloacetate + Glutamate <-> Aspartate + -ketoglutarate (Urea cycle)

Example aminotransferase enzymes include the serum glutamate-oxaloacetate transaminase (SGOT) and serum glutamate-pyruvate transaminase (SGPT).

See also: Transamination in Amino Acid Metabolism, Amino Acids, -Ketoglutarate, De Novo Biosynthesis of Purine Nucleotides

INTERNET LINK: Urea Cycle and Metabolism of Amino Groups