Histidine Decarboxylase

Histidine decarboxylase (HDC) is the enzyme that catalyzes the reaction that produces histamine from histidine with the help of vitamin B6 as follows:

Known inhibitors of histidine decarboxylase : catechin, tritoqualine an atypical antihistaminic (Hypostamin©).

C6H9N3O2 → C5H9N3 + CO2

In humans, the histidine decarboxylase enzyme is encoded by the HDC gene.

The biogenic amine histamine is an important modulator of numerous physiologic processes, including neurotransmission, gastric acid secretion, and smooth muscle tone. The biosynthesis of histamine from histidine is catalyzed by the enzyme L-histidine decarboxylase. This homodimeric enzyme is a pyridoxal phosphate (PLP)-dependent decarboxylase and is highly specific for its histidine substrate.

Some mutations in the gene for this enzyme can cause symptoms of Tourette syndrome; however, these mutations have only been observed in one family and are not thought to account for most cases of Tourette syndrome.

In bacteria, it is synthesised as a proenzyme, PI. Cleavage of the proenzyme PI chain yields two subunits, alpha and beta, which arrange as a hexamer, (alpha beta)6, by nonhydrolytic self-catalysis.

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