FAICAR => IMP + H2O

The reversible synthesis of inosine 5'-monophosphate from 5'-phosphoribosyl-5-formaminoimidazole-4-carboxamide (FAICAR) is catalyzed by the IMP cyclohydrolase activity of the bifunctional 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase enzyme. This cytosolic protein occurs primarily as a dimer (Rayl et al. 1996; Vergis et al. 2001) and may further associate with other enzymes of de novo IMP biosynthesis under some metabolic conditions (An et al. 2008).

5'-单磷酸肌苷的可逆合成由双功能5-氨基咪唑-4-羧酰胺核糖核苷酸甲酰转移酶/IMP环化水合酶酶的IMP环化水合酶活性催化而成。此细胞质蛋白主要以二聚体形式存在（Rayl等，1996；Vergis等，2001），在某些代谢条件下，还可能进一步与从头合成IMP的生物合成相关酶相互结合（An等，2008）。