Transaminaatioon

Transaminaatioon is the biochemical process in which an amino group from an amino acid is transferred to a keto acid, forming a new amino acid and a new alpha-keto acid. This reaction is catalyzed by enzymes called aminotransferases or transaminases and requires vitamin B6 in the form of pyridoxal phosphate (PLP) as a coenzyme. Transaminaatioon is typically reversible and plays a central role in both the degradation and synthesis of amino acids, enabling interconversion among amino acids and their corresponding keto acids and contributing to overall nitrogen metabolism.

Common transamination reactions include alanine transamination, where alanine reacts with alpha-ketoglutarate to form pyruvate and glutamate, and aspartate transamination, where aspartate reacts with alpha-ketoglutarate to form oxaloacetate and glutamate. These reactions proceed through a ping-pong bi-bi mechanism involving PLP, and the balance of substrates and products helps determine the flow of nitrogen in the cell.

Localization varies among transaminases. Some are cytosolic, such as alanine aminotransferase (ALT), while others are mitochondrial, such as aspartate aminotransferase (AST). In clinical biochemistry, ALT and AST are measured as liver-enzyme indicators; elevated levels can indicate hepatocellular injury, though AST is also present in heart and skeletal muscle, making the AST/ALT ratio diagnostically informative in certain contexts.

Beyond human physiology, transaminaatioon is essential in other organisms for amino acid biosynthesis and nitrogen assimilation. It also serves to transfer amino groups without releasing free ammonia, which may be incorporated into other metabolic pathways.