Tryptophan hydroxylase

Tryptophan Hydroxylase (TPH) is an enzyme that is involved in the biosynthesis of the neurotransmitter serotonin. It is the rate-limiting enzyme in the pathway, meaning that it is the slowest and thus determines the overall speed of serotonin production. TPH uses the amino acid tryptophan as a substrate to produce 5-hydroxytryptophan, which is then converted into serotonin by the enzyme aromatic L-amino acid decarboxylase.

Function

Tryptophan hydroxylase is one of the several key enzymes in the body's biosynthesis of serotonin. It is a member of the aromatic amino acid hydroxylase (AAAH) family, which also includes phenylalanine hydroxylase and tyrosine hydroxylase. These enzymes incorporate one of the atoms of molecular oxygen into their substrates, a process known as hydroxylation.

Structure

Tryptophan hydroxylase exists in two isoforms: TPH1 and TPH2. TPH1 is primarily found in the pineal gland and the peripheral nervous system, while TPH2 is mainly expressed in the brainstem. Both isoforms are identical in their catalytic activity but differ in their expression patterns and regulation.

Clinical significance

Alterations in the function of tryptophan hydroxylase have been linked to a variety of disorders, including depression, anxiety, and obsessive-compulsive disorder. In particular, reduced activity of TPH2 in the brain has been associated with increased susceptibility to these conditions. Additionally, certain genetic variants of the TPH genes have been found to be associated with increased risk of suicidal behavior.

See also

• Serotonin
• Tryptophan
• 5-Hydroxytryptophan
• Aromatic L-amino acid decarboxylase
• Phenylalanine hydroxylase
• Tyrosine hydroxylase

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