Uroporphyrinogen III

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Uroporphyrinogen III
Uroporphyrinogen III skeletal.svg
MeSH Uroporphyrinogen+III
Molar mass 836.795 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Uroporphyrinogen III is a tetrapyrrole, the first macrocyclic intermediate in the biosynthesis of heme, chlorophyll, vitamin B12, and siroheme. It is a colorless compound, like other porphyrinogens.

Biosynthetic context[edit]


Its biosynthetic precursor is the linear tetrapyrrole hydroxymethylbilane, which is converted to uroporphyrinogen III by the action of uroporphyrinogen-III synthase.[1] If, however, uroporphyrinogen-III synthase is not present, the hydroxymethylbilane will spontaneously cyclise into uroporphyrinogen I. The difference between the uroporphyrinogen I and III is the arrangement of the four propionic acid ("P" groups) and the four acetic acid groups ("A" groups). Uroporphyrinogen I features in an AP-AP-AP-AP symmetry, whereas in uroporphyrinogen III one AP-group is reversed and hence an AP-AP-AP-PA arrangement.

Conversion to heme and sirohemes, etc.[edit]

In the biosynthesis of sirohemes, uroporphyrinogen III is converted by two methyl transferases to dihydrosirohydrochlorin, which is subsequently oxidized sirohydrochlorin, a precursor to the siroheme prosthetic group. In the biosynthesis of hemes and chlorophylls, uroporphyrinogen III is converted into coproporphyrinogen III by the enzyme uroporphyrinogen III decarboxylase.

See also[edit]


  1. ^ Paul R. Ortiz de Montellano (2008). "Hemes in Biology". Wiley Encyclopedia of Chemical Biology. John Wiley & Sons. doi:10.1002/9780470048672.wecb221.
Heme synthesis—note that some reactions occur in the cytoplasm and some in the mitochondrion (yellow)