transaminaasit

Transaminaasit, commonly referred to as transaminases or aminotransferases, are a group of enzymes that catalyze transamination reactions. In these reactions, an amino group is transferred from an amino acid to a corresponding α-keto acid, allowing the interconversion of amino acids and keto acids. Transaminases use pyridoxal phosphate, the active form of vitamin B6, as a cofactor and typically operate in a reversible manner.

The two best-known human transaminases are alanine transaminase (ALT, also called GPT) and aspartate transaminase (AST, also called GOT). ALT catalyzes the reaction of L-alanine with α-ketoglutarate to form pyruvate and L-glutamate, while AST catalyzes L-aspartate with α-ketoglutarate to form oxaloacetate and L-glutamate. In humans, AST exists in cytosolic and mitochondrial forms, whereas ALT is predominantly cytosolic. Transaminases play a central role in amino acid metabolism and nitrogen transport, and they contribute to gluconeogenesis by generating substrates for carbohydrate metabolism.

Physiologically, ALT is more liver-specific, while AST is distributed in liver, heart, skeletal muscle, kidney, and brain. Because of this distribution, elevated serum levels of these enzymes typically reflect tissue injury in the involved organs. Clinically, ALT and AST are measured as part of liver function tests; the ratio of AST to ALT (the De Ritis ratio) can aid in differential diagnosis, such as distinguishing alcoholic liver disease from viral hepatitis or other hepatic conditions.

Transaminaasit activity can be influenced by vitamin B6 status and certain drugs. Their measurement provides diagnostic information but must be interpreted within the broader clinical context.