Uroporphyrinogens are cyclic tetrapyrroles with four

propionic acid Propionic acid (, from the Greek words πρῶτος : ''prōtos'', meaning "first", and πίων : ''píōn'', meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula CH3CH2CO2H. It is a liq ...

groups ("P" groups) and four

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...

groups ("A" groups). There are four forms, which vary based upon the arrangements of the "P" and "A" groups (in clockwise order): * In the "I" variety (i.e.

uroporphyrinogen I Uroporphyrinogen I is an isomer of uroporphyrinogen III, a metabolic intermediate in the biosynthesis of heme. A type of porphyria is caused by production of uroporphyrinogen I instead of III. Biosynthesis and metabolism In living organisms, uro ...

), the order repeats four times: AP-AP-AP-AP. * In the "III" variety (i.e. uroporphyrinogen III), the fourth is reversed: AP-AP-AP-PA. *:This is the most common form. In the synthesis of porphyrin, it is created from the linear tetrapyrrole

hydroxymethylbilane Hydroxymethylbilane, also known as preuroporphyrinogen, is an organic compound that occurs in living organisms during the synthesis of porphyrins, a group of critical substances that include haemoglobin, myoglobin, and chlorophyll. The name is ofte ...

by the enzyme

uroporphyrinogen III synthase Uroporphyrinogen III synthase () is an enzyme involved in the metabolism of the cyclic tetrapyrrole compound porphyrin. It is involved in the conversion of hydroxymethyl bilane into uroporphyrinogen III. This enzyme catalyses the inversion of t ...

, and is further converted into coproporphyrinogen III by the enzyme

uroporphyrinogen III decarboxylase Uroporphyrinogen III decarboxylase (uroporphyrinogen decarboxylase, or UROD) is an enzyme () that in humans is encoded by the ''UROD'' gene. Function Uroporphyrinogen III decarboxylase is a homodimeric enzyme () that catalyzes the fifth step i ...

. * The "II" and "IV" varieties can be created synthetically, but do not appear in nature.

External links

* Biomolecules {{biochem-stub