Uroporphyrinogen decarboxylase (URO-D) is a dimeric cytosolic enzyme that decarboxylates the four acetate side chains of uroporphyrinogen III (uro-III) to create coproporphyrinogen III, without requiring any prosthetic groups or cofactors. This reaction is located at the branching point of the tetrapyrrole biosynthetic pathway, leading to the biosynthesis of heme, chlorophyll or bacteriochlorophyll. URO-D deficiency is responsible for the human genetic diseases familial porphyria cutanea tarda (fPCT) and hepatoerythropoietic porphyria (HEP).
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