Tryptophan hydroxylase 1 (TPH1) is an
isoenzyme In biochemistry, isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. dif ...
of
tryptophan hydroxylase
Tryptophan hydroxylase (TPH) is an enzyme () involved in the synthesis of the neurotransmitter serotonin. Tyrosine hydroxylase, phenylalanine hydroxylase, and tryptophan hydroxylase together constitute the family of biopterin-dependent aro ...
which in humans is encoded by the ''TPH1''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
TPH1 was first discovered to synthesize
serotonin in 1988
and was thought that there only was a single ''TPH'' gene until 2003, while a second form was found in the mouse (''Tph2''), rat and human brain (
TPH2
Tryptophan hydroxylase 2 (TPH2) is an isozyme of tryptophan hydroxylase found in vertebrates. In humans, TPH2 is primarily expressed in the serotonergic neurons of the brain, with the highest expression in the raphe nucleus of the midbrain. Until ...
) and the original TPH was then renamed to TPH1.
Function
Tryptophan hydroxylases catalyze the
biopterin
Biopterins are pterin derivatives which function as endogenous enzyme Cofactor (biochemistry), cofactors in many species of animals and in some bacteria and fungi. The prototypical compound of the class is biopterin (6-(1,2-dihydroxypropyl)-pterin) ...
-dependent monooxygenation of
tryptophan
Tryptophan (symbol Trp or W)
is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α- carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...
to
5-hydroxytryptophan (5-HTP), which is subsequently
decarboxylated to form the neurotransmitter
serotonin (5-hydroxytryptamine or 5-HT). It is the rate-limiting enzyme in the biosynthesis of serotonin.
TPH expression is limited to a few specialized tissues:
raphe
Raphe (; from Greek ῥαφή, "seam"Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press.) has several diffe ...
neurons,
pinealocyte
Pinealocytes are the main cells contained in the pineal gland, located behind the third ventricle and between the two hemispheres of the brain. The primary function of the pinealocytes is the secretion of the hormone melatonin, important in th ...
s,
mast cell
A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a par ...
s, mononuclear
leukocytes,
beta-cells
Beta cells (β-cells) are a type of cell found in pancreatic islets that synthesize and secrete insulin and amylin. Beta cells make up 50–70% of the cells in human islets. In patients with Type 1 diabetes, beta-cell mass and function are dimi ...
of the islets of Langerhans, and intestinal and pancreatic
enterochromaffin cell
Enterochromaffin (EC) cells (also known as Kulchitsky cells) are a type of enteroendocrine cell, and neuroendocrine cell. They reside alongside the epithelium lining the lumen of the digestive tract and play a crucial role in gastrointestinal reg ...
s.
Clinical significance
Tryptophan hydroxylase
Tryptophan hydroxylase (TPH) is an enzyme () involved in the synthesis of the neurotransmitter serotonin. Tyrosine hydroxylase, phenylalanine hydroxylase, and tryptophan hydroxylase together constitute the family of biopterin-dependent aro ...
is important for synthesizing
indoleamine
Indolamines are a family of neurotransmitters that share a common molecular structure (namely, indolamine). Indolamines are a classification of monoamine neurotransmitter, along with catecholamines and ethylamine derivatives. A common example o ...
neurotransmitters and related compounds in the body and
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
, including serotonin,
melatonin,
tryptamine
Tryptamine is an indolamine metabolite of the essential amino acid, tryptophan. The chemical structure is defined by an indole ─ a fused benzene and pyrrole ring, and a 2-aminoethyl group at the second carbon (third aromatic atom, with the f ...
,
N-methyltryptamine
''N''-Methyltryptamine (NMT) is a member of the substituted tryptamine chemical class and a natural product which is biosynthesized in the human body from tryptamine by certain N-methyltransferase enzymes, such as indolethylamine ''N''-methyl ...
, and
N,N-dimethyltryptamine
''N'',''N''-Dimethyltryptamine (DMT or ''N'',''N''-DMT, SPL026) is a substituted tryptamine that occurs in many plants and animals, including human beings, and which is both a derivative and a structural analog of tryptamine. It is used as ...
. TPH1 is expressed in the body, but not the brain.
Nevertheless, the effect of variations in the TPH1
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
on brain-related variables, such as
personality trait
In psychology, trait theory (also called dispositional theory) is an approach to the study of human personality. Trait theorists are primarily interested in the measurement of ''traits'', which can be defined as habitual patterns of behaviour, tho ...
s and
neuropsychiatric disorder
A mental disorder, also referred to as a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features may be persistent, relapsing and remitti ...
s, has been studied.
For example, one study (1998) found an association between a
polymorphism in the gene with
impulsive-
aggression measures,
while a
case-control study (2001) could find no association between polymorphisms and
Alzheimer's disease
Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...
.
One human mutant of TPH1, A218C found in
intron 7, is highly associated with schizophrenia.
Introns are regions of DNA that do not code for the amino acid sequence of a protein and were long considered to be 'junk DNA' lacking purpose. The correlation of an intron mutation with schizophrenia is significant because it suggests that introns have an important role in
translation
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
,
transcription
Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including:
Genetics
* Transcription (biology), the copying of DNA into RNA, the fir ...
, or another, possibly unknown, aspect of the production of proteins from DNA.
See also
*
Tryptophan hydroxylase
Tryptophan hydroxylase (TPH) is an enzyme () involved in the synthesis of the neurotransmitter serotonin. Tyrosine hydroxylase, phenylalanine hydroxylase, and tryptophan hydroxylase together constitute the family of biopterin-dependent aro ...
*
TPH2
Tryptophan hydroxylase 2 (TPH2) is an isozyme of tryptophan hydroxylase found in vertebrates. In humans, TPH2 is primarily expressed in the serotonergic neurons of the brain, with the highest expression in the raphe nucleus of the midbrain. Until ...
*
Rs1799913
In genetics, rs1799913, also called A779C, is a gene variation—a single nucleotide polymorphism (SNP)— in the TPH1 gene.
It is located in intron 7.
The SNP association with schizophrenia has been examined in several studies, though a ...
(A779C): intron related to figural and numeric creativity
*
rs1800532
In genetics, rs1800532 (A218C) is a genetic variant.
It is a single nucleotide polymorphism in the ''TPH1'' gene and located in intron 7.
It has been examined in relation to personality trait
In psychology, trait theory (also called dispositio ...
(A218C)
References
Further reading
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External links
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