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|tryptophan hydroxylase 1 (tryptophan 5-monooxygenase)|
|Symbol(s):||TPH1 TPRH, TPH|
|Locus:||11 p15.3 -p14|
|tryptophan hydroxylase 2|
The "activity" of tryptophan hydroxylase (i.e. the rate it converts L-tryptophan into the serotonin precursor L-5-hydroxytryptophan) can be increased when it undergoes phosphorylation. Protein Kinase A, for example, can phosphorylate tryptophan hydroxylase, thus increasing its activity. This phosphorylation is of particular interest, because in the 2 major steps to serotonin production (L-tryptophan to L-5-hydroxytryptophan to 5-hydroxytryptamine [serotonin]), the first step - involving tryptophan hydroxylase - is the rate limiting step.
In humans, as well as in other mammals, there are two isoforms of this enzyme. These isoforms are termed 1 and 2 and derive from two different, but homologous, genes.
- TPH1 is mostly expressed in tissues that express serotonin in the periphery (skin, gut, pineal gland) but it is also expressed in the central nervous system.
- On the other hand, TPH2 is exclusively expressed in neuronal cell types and is the predominant isoform in the central nervous system.
- REDIRECT Template:Dioxygenases