Ma Zhongxin, Williamson Heather R, Davidson Victor L
Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, U.S.A.
Biochem J. 2016 Jun 15;473(12):1769-75. doi: 10.1042/BCJ20160047. Epub 2016 Apr 13.
In the absence of its substrate, the auto-reduction of the high-valent bis-Fe(IV) state of the dihaem enzyme MauG is coupled to oxidative damage of a methionine residue. Transient kinetic and solvent isotope effect studies reveal that this process occurs via two sequential long-range electron transfer (ET) reactions from methionine to the haems. The first ET is coupled to proton transfer (PT) to the haems from solvent via an ordered water network. The second ET is coupled to PT at the methionine site and occurs during the oxidation of the methionine to a sulfoxide. This process proceeds via Compound I- and Compound II-like haem intermediates. It is proposed that the methionine radical is stabilized by a two-centre three-electron (2c3e) bond. This provides insight into how oxidative damage to proteins may occur without direct contact with a reactive oxygen species, and how that damage can be propagated through the protein.
在缺乏底物的情况下，双血红素酶MauG的高价双铁（IV）状态的自动还原与甲硫氨酸残基的氧化损伤相关联。瞬态动力学和溶剂同位素效应研究表明，该过程通过从甲硫氨酸到血红素的两个连续的长程电子转移（ET）反应发生。第一次电子转移与质子转移（PT）耦合，质子通过有序水网络从溶剂转移到血红素。第二次电子转移与甲硫氨酸位点的质子转移耦合，发生在甲硫氨酸氧化为亚砜的过程中。这个过程通过类似化合物I和化合物II的血红素中间体进行。有人提出，甲硫氨酸自由基通过双中心三电子（2c3e）键得以稳定。这为蛋白质如何在不与活性氧直接接触的情况下发生氧化损伤以及这种损伤如何在蛋白质中传播提供了见解。
