Tasca Federico, Gorton Lo, Harreither Wolfgang, Haltrich Dietmar, Ludwig Roland, Nöll Gilbert
Department of Analytical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
Anal Chem. 2009 Apr 1;81(7):2791-8. doi: 10.1021/ac900225z.
Direct and mediated electron transfer (DET and MET) between the enzyme and electrodes were compared for cellobiose dehydrogenase (CDH) from the basidiomycete Phanerochaete sordida (PsCDH). For DET, PsCDH was adsorbed at pyrolytic graphite (PG) electrodes while for MET the enzyme was covalently linked to a low potential Os redox polymer. Both types of electrodes were prepared in the presence of single walled carbon nanotubes (SWCNTs). DET requires the oxidation of the heme domain, while MET occurs partially via the heme and the flavin domain at pH 3.5. At pH 6 MET occurs solely via the flavin domain. Most probably, the interaction of the domains decreases from pH 3.5 to 6.0 due to electrostatic repulsion of deprotonated amino acid residues, covering the surfaces of both domains. MET starts at a lower potential than DET. The midpoint potentials at pH 3.5 for the flavin (40 mV) and the heme domain (170 mV) were determined with spectroelectrochemistry. The electrochemical and spectroelectrochemical measurements presented in this work are in conformity. The pH dependency of DET and MET was investigated for PsCDH. The optimum was observed between pH 4 and 4.5 pH for DET and in the range of pH 5-6 for MET. The current densities obtained by MET are 1 order of magnitude higher than by DET. During multicycle cyclic voltammetry experiments carried out at different pHs, the PsCDH modified electrode working by MET turned out to be very stable. In order to characterize a PsCDH modified anode working by MET with respect to biofuel cell applications, this electrode was combined with a Pt-black cathode as model for a membraneless biofuel cell. In comparison to DET, a 10 times higher maximum current and maximum power density in a biofuel cell application could be achieved by MET. While CDH modified electrodes working by DET are highly qualified for applications in amperometric biosensors, a much better performance as biofuel cell anodes can be obtained by MET. The use of CDH modified electrodes working by MET for biofuel cell applications results in a less positive onset of the electrocatalytic current (which may lead to an increased cell voltage), higher current and power density, and much better long-term stability over a broad range of pH.
对担子菌污色多孔菌（PsCDH）的纤维二糖脱氢酶（CDH），比较了酶与电极之间的直接电子转移（DET）和介导电子转移（MET）。对于DET，将PsCDH吸附在热解石墨（PG）电极上，而对于MET，该酶与低电位的锇氧化还原聚合物共价连接。两种类型的电极均在单壁碳纳米管（SWCNT）存在下制备。DET需要血红素结构域氧化，而MET在pH 3.5时部分通过血红素和黄素结构域发生。在pH 6时，MET仅通过黄素结构域发生。很可能，由于去质子化氨基酸残基的静电排斥，两个结构域的表面被覆盖，从pH 3.5到6.0，结构域之间的相互作用减弱。MET比DET在更低的电位开始。用光谱电化学法测定了pH 3.5时黄素（40 mV）和血红素结构域（170 mV）的中点电位。本文给出的电化学和光谱电化学测量结果是一致的。研究了PsCDH的DET和MET对pH的依赖性。观察到DET在pH 4至4.5之间有最佳值，MET在pH 5 - 6范围内有最佳值。MET获得的电流密度比DET高1个数量级。在不同pH下进行多循环循环伏安实验时，通过MET工作的PsCDH修饰电极非常稳定。为了表征通过MET工作的用于生物燃料电池应用的PsCDH修饰阳极，将该电极与作为无膜生物燃料电池模型的铂黑阴极组合。与DET相比，MET在生物燃料电池应用中可实现高10倍的最大电流和最大功率密度。虽然通过DET工作的CDH修饰电极非常适合用于电流型生物传感器，但通过MET可获得作为生物燃料电池阳极更好的性能。将通过MET工作的CDH修饰电极用于生物燃料电池应用会导致电催化电流的起始电位更正（这可能导致电池电压升高）、更高的电流和功率密度，以及在很宽的pH范围内更好的长期稳定性。
