PDF(Pubmed)
Abstract：
Bacillus subtilis ferredoxin:NADP+ oxidoreductase (BsFNR) is a thioredoxin reductase-type FNR whose redox properties and reactivity with nonphysiological electron acceptors have been scarcely characterized. On the basis of redox reactions with 3-acetylpyridine adenine dinucleotide phosphate, the two-electron reduction midpoint potential of the flavin adenine dinucleotide (FAD) cofactor was estimated to be -0.240 V. Photoreduction using 5-deazaflavin mononucleotide (5-deazaFMN) as a photosensitizer revealed that the difference in the redox potentials between the first and second single-electron transfer steps was 0.024 V. We examined the mechanisms of the reduction of several different groups of non-physiological electron acceptors catalyzed by BsFNR. The reactivity of quinones and aromatic N-oxides toward BsFNR increased when increasing their single-electron reduction midpoint redox potentials. The reactivity of nitroaromatic compounds was lower due to their lower electron self-exchange rate, but it exhibited the same trend. A mixed single- and two-electron reduction reaction was characteristic of quinones, whereas reactions involving nitroaromatics proceeded exclusively via the one-electron reduction reaction. The oxidation of FADH• to FAD is the rate-limiting step during the oxidation of fully reduced FAD. The calculated electron transfer distances in the reaction with nitroaromatics were close to those of other FNRs including the plant-type enzymes, thus demonstrating their similar active site accessibility to low-molecular-weight oxidants despite the fundamental differences in their structures.
摘要：
枯草芽孢杆菌铁氧还蛋白：NADP氧化还原酶（BsFNR）是硫氧还蛋白还原酶型FNR，其氧化还原特性和与非生理电子受体的反应性几乎没有表征。根据与3-乙酰吡啶腺嘌呤二核苷酸磷酸的氧化还原反应，黄素腺嘌呤二核苷酸（FAD）辅因子的两电子还原中点电位估计为-0.240V。使用5-脱氮黄素单核苷酸（5-脱氮FMN）作为光敏剂的光还原表明，第一和第二单电子转移步骤之间的氧化还原电位差异为0.024V。醌和芳香族N-氧化物对BsFNR的反应性当增加其单电子还原中点氧化还原电位时增加。硝基芳族化合物的反应性较低，由于它们的电子自交换速率较低，但它表现出同样的趋势。混合的单电子和双电子还原反应是醌的特征，而涉及硝基芳烃的反应仅通过单电子还原反应进行。FADH氧化为FAD是完全还原的FAD氧化过程中的限速步骤。与硝基芳烃反应中计算的电子转移距离接近其他FNR，包括植物型酶，因此，尽管它们的结构存在根本差异，但它们对低分子量氧化剂的活性位点可及性相似。
