Redox Reactions of Reduced Flavin Mononucleotide (FMN), Riboflavin (RBF), and Anthraquinone-2,6-disulfonate (AQDS) with Ferrihydrite and Lepidocrocite
Redox Reactions of Reduced Flavin Mononucleotide (FMN), Riboflavin (RBF), and Anthraquinone-2,6-disulfonate (AQDS) with Ferrihydrite and Lepidocrocite
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DOI：
10.1021/es301544b
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发表时间：
2012-11-06
影响因子：
11.4
通讯作者：
Fredrickson, Jim K.
中科院分区：
文献类型：
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作者：
Shi, Zhi;Zachara, John M.;Fredrickson, Jim K.
黄素是由异化铁还原菌希瓦氏菌分泌的，可以作为内源性电子传递介质。为了评估黄素在Fe（III）生物还原中的潜在重要性，我们研究了还原的黄素单苷脂的氧化还原反应动力学（即，FMNH 2）和还原型核黄素（即，RBFH 2）与水铁矿和纤铁矿。有机还原剂在pH 4-8范围内迅速还原并溶解水铁矿和纤铁矿。FMNH 2对2线水铁矿还原溶解的速率常数k为87.5 +/- 3.5 M-1。s（-1），RBFH_2的k值与之相似。对于纤铁矿，FMNH 2和236 +/- 22 M-1的k分别为500 +/- 61 M-1.s（-1）。s（-1）对于RBFH 2。表面积归一化的初始反应速率（r（a））为0.08和77 μ mol·m（-2）·s（-1）之间的各种条件下，在停止流动实验。初始速率（r（o））是一阶相对于氧化铁（III）的浓度，和r（a）随pH值的降低而增加。结晶不良2线水铁矿产生最高的r（a），其次是更多的结晶6线水铁矿和结晶lepidocrotite。与先前对希瓦氏菌菌株MR-1的全细胞研究相比，我们的发现表明Mtr减少电子传递介质（即，金属还原）途径是速率限制的，而不是非均相电子转移到氧化铁（III）。
Flavins are secreted by the dissimilatory iron-reducing bacterium Shewanella and can function as endogenous electron transfer mediators. To assess the potential importance of flavins in Fe(III) bioreduction, we investigated the redox reaction kinetics of reduced flavin mononucleotide, (i.e., FMNH2) and reduced riboflavin (i.e., RBFH2) with ferrihydrite and lepidocrocite. The organic reductants rapidly reduced and dissolved ferrihydrite and lepidocrocite in the pH range 4-8. The rate constant k for 2-line ferrihydrite reductive dissolution by FMNH2 was 87.5 +/- 3.5 M-1. s(-1) at pH 7.0 in batch reactors, and k was similar for RBFH2. For lepidocrocite, k was 500 +/- 61 M-1.s(-1) for FMNH2 and 236 +/- 22 M-1 . s(-1) for RBFH2. The surface area normalized initial reaction rates (r(a)) were between 0.08 and 77 mu mol.m(-2).s(-1) for various conditions in stopped flow experiments. Initial rates (r(o)) were first order with respect to iron(III) oxide concentration, and r(a) increased with decreasing pH. Poorly crystalline 2-line ferrihydrite yielded the highest r(a), followed by more crystalline 6-line ferrihydrite and crystalline lepidocrocite. Compared to a previous whole-cell study with Shewanella oneidensis strain MR-1, our findings suggest that the reduction of electron transfer mediators by the Mtr (i.e., metal-reducing) pathway coupled to lactate oxidation is rate limiting, rather than heterogeneous electron transfer to the iron(III) oxide.