McGuire Ashlyn H, Carey Leiah M, de Serrano Vesna, Dali Safaa, Ghiladi Reza A
Department of Chemistry , North Carolina State University , Raleigh , North Carolina 27695-8204 , United States.
Biochemistry. 2018 Jul 31;57(30):4455-4468. doi: 10.1021/acs.biochem.8b00540. Epub 2018 Jul 13.
The dehaloperoxidase-hemoglobin (DHP) from the terebellid polychaete Amphitrite ornata is a multifunctional hemoprotein that catalyzes the oxidation of a wide variety of substrates, including halo/nitrophenols, haloindoles, and pyrroles, via peroxidase and/or peroxygenase mechanisms. To probe whether substrate substituent effects can modulate enzyme activity in DHP, we investigated its reactiviy against a panel of o-guaiacol substrates given their presence (from native/halogenated and non-native/anthropogenic sources) in the benthic environment that A. ornata inhabits. Using biochemical assays supported by spectroscopic, spectrometric, and structural studies, DHP was found to catalyze the HO-dependent oxidative dehalogenation of 4-haloguaiacols (F, Cl, and Br) to 2-methoxybenzoquinone (2-MeOBQ). O labeling studies confirmed that O atom incorporation was derived exclusively from water, consistent with substrate oxidation via a peroxidase-based mechanism. The 2-MeOBQ product further reduced DHP to its oxyferrous state, providing a link between the substrate oxidation and O carrier functions of DHP. Nonnative substrates resulted in polymerization of the initial substrate with varying degrees of oxidation, with 2-MeOBQ identified as a minor product. When viewed alongside the reactivity of previously studied phenolic substrates, the results presented here show that simple substituent effects can serve as functional switches between peroxidase and peroxygenase activities in this multifunctional catalytic globin. More broadly, when recent findings on DHP activity with nitrophenols and azoles are included, the results presented here further demonstrate the breadth of heterocyclic compounds of anthropogenic origin that can potentially disrupt marine hemoglobins or function as environmental stressors, findings that may be important when assessing the environmental impact of these pollutants (and their metabolites) on aquatic systems.
来自多毛纲缨鳃虫的脱卤过氧化物酶-血红蛋白（DHP）是一种多功能血红蛋白，它通过过氧化物酶和/或加氧酶机制催化多种底物的氧化，这些底物包括卤代/硝基酚、卤代吲哚和吡咯。为了探究底物取代基效应是否能调节DHP中的酶活性，我们研究了它对一组邻甲氧基苯酚底物的反应活性，因为这些底物存在于缨鳃虫栖息的底栖环境中（既有天然/卤代来源的，也有非天然/人为来源的）。通过光谱、光谱测定和结构研究支持的生化分析，发现DHP催化4-卤代邻甲氧基苯酚（F、Cl和Br）依赖HO的氧化脱卤反应生成2-甲氧基苯醌（2-MeOBQ）。O标记研究证实，O原子的掺入完全来自水，这与基于过氧化物酶机制的底物氧化一致。2-MeOBQ产物进一步将DHP还原为亚铁氧合状态，这为DHP的底物氧化和O载体功能之间提供了联系。非天然底物导致初始底物发生不同程度氧化的聚合反应，2-MeOBQ被鉴定为次要产物。与之前研究的酚类底物的反应活性一起考虑时，本文给出的结果表明，简单的取代基效应可以作为这种多功能催化球蛋白中过氧化物酶和加氧酶活性之间的功能开关。更广泛地说，当纳入最近关于DHP对硝基酚和唑类的活性的研究结果时，本文给出的结果进一步证明了人为来源的杂环化合物的范围，这些化合物可能会破坏海洋血红蛋白或作为环境应激源，这些发现对于评估这些污染物（及其代谢物）对水生系统的环境影响可能很重要。
