Serotonin (5-HT)

• Serotonin (5-HT) is a chemical messenger (neurotransmitter) primarily found in the brain, blood platelets, and the digestive system.
• It plays a key role in regulating mood, emotion, sleep, appetite, digestion, and various other physiological functions.
• Serotonin is synthesized from the amino acid tryptophan and is often associated with feelings of well-being and happiness.

Synthesis of Serotonin (5-HT):

• Step 1: Conversion to 5-Hydroxytryptophan (5-HTP):
  • Enzyme: Tryptophan hydroxylase
  • Process: The enzyme tryptophan hydroxylase catalyzes the hydroxylation of tryptophan, an essential amino acid, converting it into 5-hydroxytryptophan (5-HTP).
  • Cofactors Required: Tetrahydrobiopterin (BH4) and oxygen.
  • Mechanism: BH4 acts as a cofactor, donating electrons, while oxygen adds a hydroxyl group (-OH) to the benzene ring of tryptophan, forming 5-HTP.
• Step 2: Conversion to Serotonin:
  • Enzyme: Aromatic L-amino acid decarboxylase (also known as DOPA decarboxylase).
  • Process: 5-HTP is decarboxylated to form serotonin (5-hydroxytryptamine, 5-HT).
  • Cofactor Required: Pyridoxal phosphate (vitamin B6).
  • Mechanism: The enzyme removes a carboxyl group (-COOH) from 5-HTP, resulting in the formation of serotonin.

Significance of Serotonin (5-HT):

1. Mood Regulation: Serotonin is crucial for maintaining mood balance and is often called the “feel-good” neurotransmitter. Low levels are associated with depression.
2. Appetite Control: It helps regulate hunger and satiety.
3. Sleep: Serotonin influences sleep cycles and is a precursor to melatonin.
4. Cognitive Functions: It aids in learning, memory, and cognitive processing.
5. Gastrointestinal Motility: Serotonin helps control bowel movements and functions.
6. Vasoconstriction: It causes the narrowing of blood vessels, which helps regulate blood flow.

Clinical Relevance:

• Psychiatric Disorders: Imbalances in serotonin levels are linked to conditions such as depression, anxiety, and obsessive-compulsive disorder (OCD)

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