Enzyme - Uroporphyrinogen decarboxylase

Alternative Name(s)
  • Uroporphyrinogen III decarboxylase.
  • Uroporphyrinogen-III carboxy-lyase.

Catalytic Activity

4 H(+) + uroporphyrinogen III = 4 CO2 + coproporphyrinogen III


There are no Cofactors for this Enzyme

Reaction Mechanism

    Uroporphyrinogen decarboxylase (HemE) catalyses the fifth step in heme biosynthesis by converting uroporphyrinogen III to coproporphyrinogen III by decarboxylating the four acetate side chains of the substrate.

    The first step in the proposed mechanism is a proton transfer from an acid (Arg37) to the C2 centre of ring D. Computational studies suggest that this first step is rate limiting. The next step is the decarboxylation of the acetate moiety. The final catalytic step in the overall mechanism is regeneration of the protonated Arg37 residue by transfer of a proton from the substrate's --C2H2-- group to its neutral guanidino group with concurrent proton transfer from the guanidinium group of Arg50 to the C3′ centre of the substrate.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Arg P06132 50 1uro 50
    Arg P06132 37 1uro 37
    Arg P06132 41 1uro 41
    Asp P06132 86 1uro 86
    Tyr P06132 164 1uro 164

Reaction Parameters

  • Kinetic Parameters
    Organism KM Value [mM] Substrate Comment
    Saccharomyces cerevisiae 0.000006 uroporphyrinogen III
    Euglena gracilis 0.00005 uroporphyrinogen III
    Homo sapiens 0.00005 5-COOH-porphyrinogen III
    Bos taurus 0.00042 6-COOH-porphyrinogen I
    Gallus gallus 0.0013 7-COOH-porphyrinogen
  • Temperature
    Organism Temperature Range Comment
    Rattus norvegicus 0 - 70 activity increases with temperature up to 47°C, decreases at 53°C
    Neohelice granulata 0 - 70 activity increases with temperature up to 47°C, decreases at 53°C
  • pH
    Organism pH Range Comment
    Homo sapiens 5 - 8 in 0.2 M KH2PO4, 0.1 mM dithiothreitol
    Oryctolagus cuniculus 5.3 - 8 pH 5.3: about 60% of maximal activity, pH 8.0: about 65% of maximal activity
    Rattus norvegicus 6 - 8
    Gallus gallus 6 - 7.4 pH 6.0: about 55% of maximal activity, pH 7.4: about 50% of maximal activity, uroporphyrinogen III
    Cereibacter sphaeroides 6.2 - 7.7 pH 6.2: about 25% of maximal activity, pH 7.7: about 70% of maximal activity

Associated Proteins

Protein name Organism
Uroporphyrinogen decarboxylase Bacillus subtilis (strain 168)
Uroporphyrinogen decarboxylase 2, chloroplastic Mouse-ear cress
Uroporphyrinogen decarboxylase, chloroplastic Maize
Uroporphyrinogen decarboxylase 1, chloroplastic Mouse-ear cress
Uroporphyrinogen III decarboxylase Nonlabens ulvanivorans