Aromatic L-amino acid decarboxylase

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Aromatic L-amino acid decarboxylase[edit | edit source]

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DOPA decarboxylase dimer structure

Aromatic L-amino acid decarboxylase (AADC), also known as DOPA decarboxylase, is an enzyme that catalyzes the decarboxylation of aromatic L-amino acids to produce their corresponding amines. This enzyme plays a crucial role in the biosynthesis of several important neurotransmitters, including dopamine, serotonin, and histamine.

Structure[edit | edit source]

Aromatic L-amino acid decarboxylase is a homodimeric enzyme, meaning it consists of two identical subunits. Each subunit contains a pyridoxal phosphate (PLP) cofactor, which is essential for the enzyme's catalytic activity. The enzyme's structure has been elucidated through X-ray crystallography, revealing details about its active site and the binding of substrates and cofactors.

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Crystal structure of aromatic L-amino acid decarboxylase

Function[edit | edit source]

AADC is responsible for the decarboxylation of L-DOPA to dopamine, 5-hydroxytryptophan to serotonin, and histidine to histamine. These reactions are critical steps in the biosynthetic pathways of these neurotransmitters, which are vital for normal neurological function.

Mechanism[edit | edit source]

The enzyme operates through a mechanism involving the formation of a Schiff base between the PLP cofactor and the substrate. This intermediate facilitates the removal of the carboxyl group from the substrate, resulting in the formation of the corresponding amine.

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Mechanism of action of aromatic L-amino acid decarboxylase

Clinical Significance[edit | edit source]

Deficiencies in AADC activity can lead to a rare genetic disorder known as AADC deficiency, characterized by a lack of dopamine and serotonin production. This condition results in severe developmental and neurological symptoms, including movement disorders and autonomic dysfunction.

Pathways[edit | edit source]

AADC is involved in several key metabolic pathways:

  • Dopamine biosynthesis: Converts L-DOPA to dopamine, a critical neurotransmitter in the central nervous system.
  • Serotonin biosynthesis: Converts 5-hydroxytryptophan to serotonin, which is involved in mood regulation and other functions.
  • Histamine biosynthesis: Converts histidine to histamine, which plays a role in immune response and gastric acid secretion.
Pathway of serotonin biosynthesis

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Contributors: Prab R. Tumpati, MD