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Tryptophan hydroxylase (TPH) is an enzyme (EC 1.14.16.4) involved in the synthesis of the monoamine neurotransmitter serotonin. Tyrosine hydroxylase, phenylalanine hydroxylase, and tryptophan hydroxylase together constitute the family of biopterin-dependent aromatic amino acid hydroxylases. TPH catalyzes the following chemical reaction
The pathway for the synthesis of serotonin from tryptophan. In animals and humans, serotonin is synthesized from the amino acid L-tryptophan by a short metabolic pathway consisting of two enzymes, tryptophan hydroxylase (TPH) and aromatic amino acid decarboxylase (DDC), and the coenzyme pyridoxal phosphate. The TPH-mediated reaction is the rate ...
Serotonin pathways are thought to modulate eating, both the amount as well as the motor processes associated with eating. The serotonergic projections into the hypothalamus are thought to be particularly relevant, and an increase in serotonergic signaling is thought to generally decrease food consumption (evidenced by fenfluramine , however ...
Dopamine Norepinephrine Serotonin. Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group connected to an aromatic ring by a two-carbon chain (such as -CH 2-CH 2-). Examples are dopamine, norepinephrine and serotonin.
In normal dopamine and serotonin (5-HT) neurotransmitter synthesis, AADC is not the rate-limiting step in either reaction. However, AADC becomes the rate-limiting step of dopamine synthesis in patients treated with L -DOPA (such as in Parkinson's disease ), and the rate-limiting step of serotonin synthesis in people treated with 5-HTP (such as ...
TPH1 was first discovered to support serotonin synthesis in 1988 by converting tryptophan into 5-hydroxytryptophan. [6] It was thought that there only was a single TPH gene until 2003. A second form was found in the mouse ( Tph2 ), rat and human brain ( TPH2 ) and the original TPH was then renamed to TPH1.
Figure 5 is a more general scheme of the reaction pathway from serotonin to melatonin. The number 2.1.1.4 refers to the Enzyme Commission Number (EC Number) for N- Acetylserotonin O-methyltransferase. These two steps are embedded in the highly involved tryptophan metabolism pathway. [13] Figure 5: Pathway serotonin → melatonin
Production of 5-HTP is the rate-limiting step in 5-HT (serotonin) synthesis. 5-HTP is normally rapidly converted to 5-HT by amino acid decarboxylase. [ 1 ] Metabolism