The redox chemistry of the covalently immobilized native and low-pH forms of yeast iso-1-cytochrome c
The redox chemistry of the covalently immobilized native and low-pH forms of yeast iso-1-cytochrome c
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DOI：
10.1021/ja0573662
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发表时间：
2006-04-26
影响因子：
15
通讯作者：
Sola, M
中科院分区：
文献类型：
--
作者：
Bortolotti, CA;Battistuzzi, G;Sola, M
对通过表面半胱氨酸形成的S-Au键固定在裸多晶金电极上的天然酿酒酵母iso-1-细胞色素c及其C102 T/N62 C变体进行了循环伏安实验。实验在不同温度（5 - 65 ℃）和pH值（1.5 - 7）下进行。在pH 7下的E-o '值（+370 mV vs SHE）比溶液中的蛋白质高约100 mV。这种差异的起源是双极性的，并提出是电极表面上密集堆积的分子之间的静电排斥的结果。在将pH降低到5（E-o '=+182mV）和3（E-o'=+71mV）以下时观察到两个另外的电化学波，这归因于两种构象异构体（分别称为"中间体"和"酸性"），其特征在于改变的血红素轴向连接。这是第一次测定的还原电位低pH值构象的细胞色素c在变性剂的情况下。由于细胞色素c的天然形式可以恢复，使pH值恢复到中性，这种转变提供的可逆调节细胞色素c的氧化还原电位的可能性对于生物电子应用是有吸引力的。固定化的C102T/N62C变体，其不同于天然蛋白质的血红素基团相对于电极的取向，显示出非常相似的还原热力学。对于这两个物种，血红素和电极之间的电子转移的速率常数增加的酸性构象，这也被发现作为一个生物催化界面的分子氧还原。
Cyclic voltammetry experiments were carried out on native Saccharomyces cerevisiae iso-1-cytochrome c and its C102T/N62C variant immobilized on bare polycrystalline gold electrode through the S-Au bond formed by a surface cysteine. Experiments were carried out at different temperatures (5-65 degrees C) and pH values (1.5-7). The E-o' value at pH 7 (+370 mV vs SHE) is approximately 100 mV higher than that for the protein in solution. This difference is enthalpic in origin and is proposed to be the result of the electrostatic repulsion among the densely packed molecules onto the electrode surface. Two additional electrochemical waves are observed upon lowering the pH below 5 (E-o' = +182 mV) and 3 (E-o', = +71 mV), which are attributed to two conformers (referred to as "intermediate" and "acidic", respectively) featuring an altered heme axial ligation. This is the first determination of the reduction potential for low-pH conformers of cytochrome c in the absence of denaturants. Since the native form of cytochrome c can be restored, bringing back the pH to neutrality, the possibility offered by this transition to reversibly modulate the redox potential of cytochrome c is appealing for bioelectronic applications. The immobilized C102T/N62C variant, which differs from the native protein in the orientation of the heme group with respect to the electrode, shows very similar reduction thermodynamics. For both species, the rate constant for electron transfer between the heme and the electrode increases for the acidic conformer, which is also found to act as a biocatalytic interface for dioxygen reduction.