UROS transforms HMB to URO3

Cytosolic uroporphyrinogen III synthase (URO3S) catalyzes the conversion of HMB (hydroxymethylbilane) to uroporphyrinogen III, a reaction involving ring closure and intramolecular rearrangement. Uroporphyrinogen III represents a branch point for the pathways leading to formation of heme, chlorophyll and corrins. HMB is rapidly converted from a linear tetrapyrrole to the cyclic form. Deficiencies of URO3S in vivo are associated with congenital erythropoietic porphyria.细胞质中尿卟啉原Ⅲ合酶（URO3S）催化HMB（羟基甲基胆烷）向尿卟啉原Ⅲ的转化，该反应涉及环闭合成和分子内重排。尿卟啉原Ⅲ是通往形成血红素、叶绿素和钴卟啉途径的一个分支点。HMB迅速从线性四吡咯转化为环状形式。体内URO3S的缺乏与先天性红细胞生成性卟啉症相关。