Woodcock S C, Warren M J
Department of Molecular Genetics, Institute of Ophthalmology, London, UK.
Biochem J. 1996 Jan 15;313 ( Pt 2)(Pt 2):415-21. doi: 10.1042/bj3130415.
CysG, also known as uroporphyrinogen III methylase and sirohaem synthase (CysG; EC 2.1.1.107), is a multifunctional enzyme that is able to transform uroporphyrinogen III into sirohaem via two S-adenosyl-L-methionine (AdoMet)-dependent transmethylations, an NAD(+)-dependent dehydrogenation and a ferrochelation. The apparent tight binding of AdoMet to this multifunctional enzyme is investigated. The use of a rapid AdoMet binding assay demonstrates that CysG becomes labelled with both [methyl-3H]AdoMet and [carboxyl-14C]AdoMet. Further experiments show that the CysG-AdoMet complex is subsequently able to methylate uroporphyrinogen III. CysG remains associated with the labelled constituents of the AdoMet even after denaturation with urea and SDS/PAGE, suggesting that the AdoMet has become covalently linked to the protein. A rapid examination of some of the other transmethylases involved in corrin biosynthesis reveals that they bind the AdoMet in a similar fashion. A multistep transmethylation mechanism is proposed to explain the observed results.
CysG，也被称为尿卟啉原III甲基转移酶和siro血红素合酶（CysG；EC 2.1.1.107），是一种多功能酶，能够通过两次依赖S-腺苷-L-甲硫氨酸（AdoMet）的甲基化、一次依赖NAD(+)的脱氢反应和一次亚铁螯合反应将尿卟啉原III转化为siro血红素。研究了AdoMet与这种多功能酶的明显紧密结合。使用快速AdoMet结合试验表明，CysG可被[甲基-3H]AdoMet和[羧基-14C]AdoMet标记。进一步的实验表明，CysG-AdoMet复合物随后能够使尿卟啉原III甲基化。即使在用尿素和SDS/PAGE变性后，CysG仍与AdoMet的标记成分结合，这表明AdoMet已与蛋白质形成共价连接。对参与钴胺素生物合成的其他一些甲基转移酶的快速检查发现，它们以类似的方式结合AdoMet。提出了一种多步甲基化机制来解释观察到的结果。
