Tryptophan-5-mono-oxygenase

Serotonin (5-hydroxytrptamine, 5-HT) synthesis involves an hydroxylation reaction (catalysed by tryptophan mono-oxygenase) and a decarboxylation step, similar to that in adrenaline (epinephrine) synthesis. 

The third kind of hydroxylase activity is the only one pertinent to the present review and refers to a mono-oxygenase of the hydroxylase type. This catalyses the insertion of a -OH group in place of a hydrogen atom at the 3-position of anthranilic acid, leading to HA. This evenience is often simply ignored by many authors dealing with tryptophan metabolism, so it could seem that the only possibility of HA formation is the action of kynureninase on HK. The actual occurrence of a true hydroxylase, as defined above, could however be considered debatable for a number of reasons, but some authors merely notice the activity without giving any reference to it. 

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