Uroporphyrinogen III decarboxylase

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Protein UROD PDB 1jph.png
Available structures
PDB Ortholog search: PDBe RCSB
Aliases UROD, PCT, UPD, uroporphyrinogen decarboxylase
External IDs OMIM: 613521 MGI: 98916 HomoloGene: 320 GeneCards: UROD
RNA expression pattern
PBB GE UROD 208970 s at fs.png

PBB GE UROD 208971 at fs.png
More reference expression data
Species Human Mouse
RefSeq (mRNA)



RefSeq (protein)



Location (UCSC) Chr 1: 45.01 – 45.02 Mb Chr 4: 116.99 – 116.99 Mb
PubMed search [1] [2]
View/Edit Human View/Edit Mouse

Uroporphyrinogen III decarboxylase (uroporphyrinogen decarboxylase, or UROD) is an enzyme (EC that in humans is encoded by the UROD gene.[3]


Uroporphyrinogen III decarboxylase is a homodimeric enzyme (PDB: 1URO​) that catalyzes the fifth step in heme biosynthesis, which corresponds to the elimination of carboxyl groups from the four acetate side chains of uroporphyrinogen III to yield coproporphyrinogen III:

uroporphyrinogen III coproporphyrinogen III + 4 CO2

Clinical significance[edit]

Mutations and deficiency in this enzyme are known to cause familial porphyria cutanea tarda and hepatoerythropoietic porphyria.[3]


At low substrate concentrations, the reaction is believed to follow an ordered route, with the sequential removal of CO2 from the D, A, B, and C rings, whereas at higher substrate/enzyme levels a random route seems to be operative. The enzyme functions as a dimer in solution, and both the enzymes from human and tobacco have been crystallized and solved at good resolutions.

The reaction catalyzed by UroD

UroD is regarded as an unusual decarboxylase, since it performs decarboxylations without the intervention of any cofactors, unlike the vast majority of decarboxylases. Its mechanism has recently been proposed to proceed through substrate protonation by an arginine residue.[4] A 2008 report demonstrated that the uncatalyzed rate for UroD's reaction is 10−19 s−1, so at pH 10 the rate acceleration of UroD relative to the uncatalyzed rate, i.e. catalytic proficiency, is the largest for any enzyme known, 6 x 1024 M−1.[5]

Proposed reaction mechanism of uroporphyrinogen III decarboxyklase


  1. ^ "Human PubMed Reference:". 
  2. ^ "Mouse PubMed Reference:". 
  3. ^ a b "Entrez Gene: UROD uroporphyrinogen decarboxylase". 
  4. ^ Silva PJ, Ramos MJ. Density-functional study of mechanisms for the cofactor-free decarboxylation performed by uroporphyrinogen III decarboxylase. J Phys Chem B 2005;109:18195-200. doi:10.1021/jp051792s.
  5. ^ Lewis CA, Wolfenden R (November 2008). "Uroporphyrinogen decarboxylation as a benchmark for the catalytic proficiency of enzymes". Proc. Natl. Acad. Sci. U.S.A. 105 (45): 17328–33. doi:10.1073/pnas.0809838105. PMC 2582308Freely accessible. PMID 18988736. 

Further reading[edit]

Heme synthesis—note that some reactions occur in the cytoplasm and some in the mitochondrion (yellow)