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Micronutrient Information Center

Overview of the tryptophan-kynurenine metabolic pathway

Pyridoxal 5'-phosphate, a vitamin B6 coenzyme, is required for the activity of several key enzymes in tryptophan catabolic pathway: KAT, KMO, and kynureninase. Dietary restriction in vitamin B6 most prominently affects kynureninase activity and results in the shift from 3-hydroxykynurenine metabolism and NAD formation to the production of kynurenic acid and xanthurenic acid. IDO, indoleamine 2,3-dioxygenase; KAT, kynurenine aminotransferase; KMO, kynurenine 3-monooxygenase; NAD, nicotinamide adenine dinucleotide; TDO, tryptophan 2,3-dioxygenase.