Tryptophan hydroxylase

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tryptophan hydroxylase 1 (tryptophan 5-monooxygenase)
Identifiers
Symbol	TPH1 TPRH, TPH
HUGO	12008
Entrez	7166
OMIM	191060
RefSeq	NM_004179
UniProt	P17752
Other data
EC number	1.14.16.4
Locus	Chr. 11 p15.3-p14

tryptophan hydroxylase 2
Identifiers
Symbol	TPH2
HUGO	20692
Entrez	121278
OMIM	607478
RefSeq	NM_173353
UniProt	Q8IWU9
Other data
Locus	Chr. 12 q15

Tryptophan hydroxylase (TPH) is an enzyme (EC 1.14.16.4) involved in the synthesis of the neurotransmitter serotonin.

1 Function
2 Isoforms
3 Additional images
4 References
5 External links

It is responsible for addition of the -OH group (hydroxylation) to the 5 position to form the amino acid 5-hydroxytryptophan (5-HTP), which is then converted to serotonin by decarboxylation:

tryptophan

5-Hydroxytryptophan

serotonin

Analogous to phenylalanine hydroxylase and tyrosine hydroxylase, this enzyme uses tetrahydrobiopterin as a co-substrate.^[1]

Tryptophan can cross the Blood-brain barrier, while Serotonin cannot. For this reason, tryptophan is administered when the desired effect is to have larger amounts of serotonin in the brain.

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 nervous 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.