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Abstract：
The biological chemistry of hydrogen sulfide (H2S) with physiologically important heme proteins is in the focus of redox biology research. In this study, we investigated the interactions of lactoperoxidase (LPO) with H2S in the presence and absence of molecular dioxygen (O2) or hydrogen peroxide (H2O2). Under anaerobic conditions, native LPO forms no heme-H2S complex upon sulfide exposure. However, under aerobic conditions or in the presence of H2O2 the formation of both ferrous and ferric sulfheme (sulfLPO) derivatives was observed based on the appearances of their characteristic optical absorptions at 638 nm and 727 nm, respectively. Interestingly, we demonstrate that LPO can catalytically oxidize H2S by H2O2 via intermediate formation of relatively short-lived ferrous and ferric sulfLPO derivatives. Pilot product analyses suggested that the turnover process generates oxidized sulfide species, which include sulfate S O 4 2 - and inorganic polysulfides ( H S x - ; x = 2-5). These results indicated that H2S can serve as a non-classical LPO substrate by inducing a reversible sulfheme-like modification of the heme porphyrin ring during turnover. Furthermore, electron paramagnetic resonance data suggest that H2S can act as a scavenger of H2O2 in the presence of LPO without detectable formation of any carbon-centered protein radical species, suggesting that H2S might be capable of protecting the enzyme from radical-mediated damage. We propose possible mechanisms, which explain our results as well as contrasting observations with other heme proteins, where either no sulfheme formation was observed or the generation of sulfheme derivatives provided a dead end for enzyme functions.
摘要：
硫化氢（H2S）与生理上重要的血红素蛋白的生物化学是氧化还原生物学研究的重点。在这项研究中,我们研究了在存在和不存在分子双氧（O2）或过氧化氢（H2O2）的情况下，乳过氧化物酶（LPO）与H2S的相互作用。在厌氧条件下,天然LPO在硫化物暴露后不形成血红素-H2S络合物。然而,在有氧条件下或在H2O2的存在下，亚铁和硫酸铁（sulfLPO）衍生物的形成是根据其在638nm和727nm处的特征光吸收的外观观察到的，分别。有趣的是,我们证明，LPO可以通过中间形成相对短寿命的亚铁和铁硫酸根LPO衍生物，通过H2O2催化氧化H2S。中试产品分析表明，周转过程会产生氧化的硫化物物种，其中包括硫酸盐SO42-和无机多硫化物(HSx-；x=2-5)。这些结果表明，H2S可以通过在周转过程中诱导血红素卟啉环的可逆的含硫血红素样修饰而充当非经典的LPO底物。此外，电子顺磁共振数据表明，在LPO存在下，H2S可以作为H2O2的清除剂，而不会形成任何碳为中心的蛋白质自由基。这表明H2S可能能够保护酶免受自由基介导的损伤。我们提出了可能的机制，这解释了我们的结果以及与其他血红素蛋白的对比观察，其中未观察到硫血红素形成或硫血红素衍生物的产生为酶功能提供了死胡同。
