Histidine decarbo, Xenopus/Amphibian,ylase (HDC) is the enzyme that catalyzes the reaction that produces histamine from histidine with the help of vitamin B6 as follows: C6H9N3O2 ? C5H9N3 + CO2. In humans, the histidine decarbo, Xenopus/Amphibian,ylase 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 decarbo, Xenopus/Amphibian,ylase. This homodimeric enzyme is a pyrido, Xenopus/Amphibian,al phosphate (PLP)-dependent decarbo, Xenopus/Amphibian,ylase and is highly specific for its histidine substrate.