hydroxymethylbilane => uroporphyrinogen III + H2O

Cytosolic UROS (uroporphyrinogen III synthase) catalyzes the reaction of hydroxymethylbilane to form uroporphyrinogen III and H2O. Chicken UROS is known only as the inferred product of a gene discovered by analysis of the chicken genomic DNA sequence. Its catalytic activity is inferred from the properties of its better-studied human counterpart.

细胞质中尿卟啉原III合酶（UROS，即尿卟啉原III合成酶）催化羟基甲基胆烷转化为尿卟啉原III和水。鸡源UROS仅作为通过分析鸡基因组DNA序列发现的基因推断产物而知名。其催化活性是通过其更为深入研究的人类同源物的特性进行推断的。