Li Qiu Ci, Mabrouk Patricia Ann
Department of Chemistry, Northeastern University, Boston, MA 02115, USA.
J Biol Inorg Chem. 2003 Jan;8(1-2):83-94. doi: 10.1007/s00775-002-0392-9. Epub 2002 Aug 30.
This paper reports the first report of rapid, reversible direct electron transfer between a redox protein, specifically, horse myoglobin, and a solid electrode substrate in nonaqueous media and the spectroscopic (UV-vis, fluorescence, and resonance Raman) characterization of the relevant redox forms of myoglobin (Mb) in dimethyl sulfoxide (DMSO). In DMSO, the heme active site of metmyoglobin (metMb) appears to remain six-coordinate high-spin, binding water weakly. Changes in the UV-fluorescence spectra for metMb in DMSO indicate that the protein secondary structure has been perturbed and suggest that helix A has moved away from the heme. UV-vis and RR spectra for deoxyMb in DMSO suggest that the heme iron is six-coordinate low-spin, most likely coordinating DMSO. Addition of CO to deoxyMb in DMSO produces a single, photostable six-coordinate CO adduct. UV-vis and RR for Mb-CO in DMSO are consistent with a six-coordinate low-spin heme iron binding His93 weakly, if at all. The polarity of the distal heme pocket is comparable to that of the closed form of horse Mb-CO in aqueous solution, pH 7. Direct electron transfer between horse Mb and Au in DMSO solution was investigated by cyclic voltammetry. Mb exhibits stable and well-defined electrochemical responses that do not appear to be affected by the water content (1.3-7.5%). The electrochemical characteristics are consistent with a one-electron, quasi-reversible, diffusion-controlled charge transfer process at Au. E degrees for horse Mb in DMSO at Au is -0.241+/-0.005 V vs. NHE. The formal heterogeneous electron transfer rate constant, calculated from delta E(p) at 20 mV/s, is 1.7+/-0.5 x 10(-4) cm/s. The rate, which is unaffected by the presence of 1.3-7.5% water, is competitive with that previously reported for horse Mb in aqueous solution.
本文报道了在非水介质中氧化还原蛋白（具体为马肌红蛋白）与固体电极底物之间快速、可逆的直接电子转移的首次报道，以及在二甲基亚砜（DMSO）中肌红蛋白（Mb）相关氧化还原形式的光谱（紫外可见光谱、荧光光谱和共振拉曼光谱）表征。在DMSO中，高铁肌红蛋白（metMb）的血红素活性位点似乎保持六配位高自旋状态，与水的结合较弱。DMSO中metMb的紫外荧光光谱变化表明蛋白质二级结构受到扰动，提示A螺旋已远离血红素。DMSO中脱氧肌红蛋白（deoxyMb）的紫外可见光谱和RR光谱表明血红素铁为六配位低自旋，最有可能与DMSO配位。向DMSO中的deoxyMb添加CO会产生单一的、光稳定的六配位CO加合物。DMSO中Mb-CO的紫外可见光谱和RR光谱与六配位低自旋血红素铁（若有结合）与His93的弱结合一致。远侧血红素口袋的极性与pH 7的水溶液中马Mb-CO的封闭形式相当。通过循环伏安法研究了DMSO溶液中马Mb与Au之间的直接电子转移。Mb表现出稳定且明确的电化学响应，似乎不受水含量（1.3 - 7.5%）的影响。电化学特性与Au上的单电子、准可逆、扩散控制的电荷转移过程一致。在DMSO中Au上的马Mb的E°相对于标准氢电极（NHE）为 -0.241±0.005 V。根据20 mV/s时的ΔE(p)计算得到的形式异相电子转移速率常数为1.7±0.5×10⁻⁴ cm/s。该速率不受1.3 - 7.5%水的存在的影响，与先前报道的水溶液中马Mb的速率具有竞争力。
