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Aminotransferases catalyze transamination in the cytosol and mitochondria of many tissues. Pyridoxal-5′-phosphate (PLP), the active form of vitamin B₆, carries the amino group during the reaction. In many reactions, α-ketoglutarate accepts the group and becomes glutamate. ALT and AST illustrate this pattern: they form pyruvate and oxaloacetate, respectively, alongside glutamate. Transamination does not release free ammonia; nitrogen can be directed toward urea formation or glutamate deamination. Its products also connect amino acid catabolism with TCA-cycle intermediates. In clinical contexts, elevated serum ALT and AST can indicate hepatocellular injury, with ALT more specific for the liver. The topic also considers amino acids that do not undergo transamination and the effects associated with PLP deficiency.