Kirk Martin L, Kc Khadanand
Met Ions Life Sci. 2020 Mar 23;20. doi: 10.1515/9783110589757-015.
The last 20 years have seen a dramatic increase in our mechanistic understanding of the reactions catalyzed by pyranopterin Mo and W enzymes. These enzymes possess a unique cofactor (Moco) that contains a novel ligand in bioinorganic chemistry, the pyranopterin ene-1,2-dithiolate. A synopsis of Moco biosynthesis and structure is presented, along with our current understanding of the role Moco plays in enzymatic catalysis. Oxygen atom transfer (OAT) reactivity is discussed in terms of breaking strong metal-oxo bonds and the mechanism of OAT catalyzed by enzymes of the sulfite oxidase (SO) family that possess dioxo Mo(VI) active sites. OAT reactivity is also discussed in members of the dimethyl sulfoxide (DMSO) reductase family, which possess des-oxo Mo(IV) sites. Finally, we reveal what is known about hydride transfer reactivity in xanthine oxidase (XO) family enzymes and the formate dehydrogenases. The formal hydride transfer reactivity catalyzed by xanthine oxidase family enzymes is complex and cleaves substrate C-H bonds using a mechanism that is distinct from monooxygenases. The chapter primarily highlights developments in the field that have occurred since ~2000, which have contributed to our collective structural and mechanistic understanding of the three canonical pyranopterin Mo enzymes families: XO, SO, and DMSO reductase.
在过去20年里，我们对吡喃蝶呤钼和钨酶催化反应的机理认识有了显著增加。这些酶拥有一种独特的辅因子（钼辅因子），其在生物无机化学中含有一种新型配体，即吡喃蝶呤-1,2-二硫烯阴离子。本文介绍了钼辅因子生物合成和结构的概要，以及我们目前对钼辅因子在酶催化中所起作用的理解。从打破强金属-氧键的角度讨论了氧原子转移（OAT）反应性，以及由具有双氧钼（VI）活性位点的亚硫酸盐氧化酶（SO）家族的酶催化的OAT机制。还讨论了具有脱氧钼（IV）位点的二甲基亚砜（DMSO）还原酶家族成员中的OAT反应性。最后，我们揭示了关于黄嘌呤氧化酶（XO）家族酶和甲酸脱氢酶中氢化物转移反应性的已知情况。黄嘌呤氧化酶家族酶催化的形式上的氢化物转移反应性很复杂，并且使用一种不同于单加氧酶的机制裂解底物的C-H键。本章主要突出了自大约2000年以来该领域的进展，这些进展有助于我们对三个典型的吡喃蝶呤钼酶家族：XO、SO和DMSO还原酶的结构和机理有共同的理解。
