Uroporphyrinogen III Synthase (UROS)

Uroporphyrinogen III synthase is also known as hydroxymethylbilane hydrolyase (cyclizing) (EC 4.2.1.75). It is the fourth enzyme in the 8-enzyme pathway in the conversion of glycine and succinyl-CoA to heme. It is responsible for the conversion of the linear tetrapyrrole, hydroxymethylbilane, to the cyclic tetrapyrrole, uroporphyrinogen III.The sequence encoded a 265-amino acid protein with a molecular mass of 28,607 Da. By Northern blot, 5-prime RACE, and multiple-tissue array analyses, Aizencang et al. (2000) demonstrated the presence of 2 UROS transcripts: an erythroid-specific transcript and a housekeeping transcript, which was present at low levels in all 76 tissues tested, with highest abundance in skeletal and heart muscle and in the caudate nucleus and amygdala.