Uroporphyrinogen III

In heme biosynthesis, joining of four porphobilinogen molecules creates a uroporphyrinogen molecule. There are two possible forms the uroporphyrinogen can have. Uroporphyrinogen III is an asymmetric compound. It arises from action of uroporphyrinogen I synthase AND urophophyrinogen III cosynthase. If only the first enzyme is active, the symmetric compound, uroporphyrinogen I is produced instead. In the hereditary condition called congenital erythropoietic porphyria, the urophophyrinogen III cosynthase is defective and the symmetric type I porphyrins accumulate, causing the urine to turn red, the skin to become photosensitive, and the teeth to become fluorescent. Since insufficient heme is produced, anemia results.

See also: Porphyrin and Heme Metabolism,

INTERNET LINKS:

> 1. Porphyrin and Chlorophyll Metabolism

> 2. Photosynthetic Pigments