Dynamics of the heterogeneous electron-transfer reaction of cytochrome c552 from Thermus thermophilus.: A time-resolved surface-enhanced resonance Raman spectroscopic study
Dynamics of the heterogeneous electron-transfer reaction of cytochrome c552 from Thermus thermophilus.: A time-resolved surface-enhanced resonance Raman spectroscopic study
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DOI：
10.1021/jp991818d
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发表时间：
1999-11-11
影响因子：
3.3
通讯作者：
Soulimane, T
中科院分区：
文献类型：
--
作者：
Lecomte, S;Hildebrandt, P;Soulimane, T
用表面增强共振拉曼（SERR）光谱研究了细胞色素C-552（Cyt-c（552））在银电极上的非均相电子转移过程。在吸附时，血红素蛋白Cyt-c（552）（其在嗜热栖热菌的呼吸链中充当电子载体）以类似于细胞色素c（Cyt-c）的两种构象状态（B1，B2）之间的电位依赖性平衡存在（Wackerbarth等人，Appl. Spectrosc. 1999，53，283）。从作为电位的函数测量的静态SERR光谱，确定状态B1的表观氧化还原电位为-0.044 V（相对于饱和甘汞电极），其比溶液中Cyt-c（552）的氧化还原电位负31 mV。的基础上的界面电位分布，占吸附的蛋白质的氧化还原位点的电位下降的模型，它的结论是，真正的气味电位的吸附状态B1是相同的血红素蛋白在溶液中。这一结论与从SERR和共振拉曼光谱的比较中得出的溶液中B1态和Cyt-c（552）的结构一致。另一方面，B2的形成与血红素口袋的实质性结构变化和氧化还原电位的大幅负移有关。采用时间分辨SERR光谱技术研究了B1的非均相还原动力学。与Cyt-c相反，发现电子转移比B2的构象转变快得多，因此可以基于一步弛豫过程来分析数据。对于形式单分子电子转移速率常数的值为4.6秒（-1）。的基础上作为超电势的函数测量的速率常数，重组能量被确定为0.15 eV。这一异常低的值可能是由于溶剂重取向对吸附物质的贡献大大减少以及Cyt-c（552）为电子转移反应优化的特定血红素口袋结构。与Cyt-c相比，Cyt-c（552）在电子传递机制和动力学上的差异显然与Cyt-c（552）独特的结构性质有关，这可能是嗜热细菌适应极端生活条件的结果。
The heterogeneous electron-transfer process of cytochrome C-552 (Cyt-c(552)) adsorbed on an Ag electrode was studied by surface-enhanced resonance Raman (SERR) spectroscopy. Upon adsorption the heme protein Cyt-c(552), which acts as an electron carrier in the respiratory chain of Thermus thermophilus, exists in a potential-dependent equilibrium between two conformational states (B1, B2) similar to cytochrome c (Cyt-c) (Wackerbarth et al. Appl. Spectrosc. 1999, 53, 283). From the stationary SERR spectra measured as a function of the potential, the apparent redox potential of state B1 was determined to be -0.044 V (versus saturated calomel electrode) which is 31 mV more negative than the redox potential of Cyt-c(552) in solution. On the basis of a model for the interfacial potential distribution that accounts for the potential drop at the redox site of the adsorbed protein, it is concluded that the true odor potential of the adsorbed state B1 is the same as that for the heme protein in solution. This conclusion is consistent with the structural identity of state B1 and Cyt-c(552) in solution that is derived from the comparison of the SERR and resonance Raman spectra. On the other hand, the formation of B2 is associated with substantial structural changes of the heme pocket and a large negative shift of the redox potential. The dynamics of the heterogeneous reduction of B1 was studied by time-resolved SERR spectroscopy which combines the spectroscopic measurements with the potential jump technique. In contrast to Cyt-c, the electron transfer was found to be much faster than the conformational transition to B2 so that the data could be analyzed on the basis of a one-step relaxation process. For the formal unimolecular electron-transfer rate constant a value of 4.6 s(-1) was obtained. On the basis of the rate constants measured as a function of the overpotential, the reorganization energy was determined to be 0.15 eV. This unusually low value may be due to a strongly diminished contribution of the solvent reorientation for the adsorbed species and the specific heme pocket structure of Cyt-c(552) optimized for the electron-transfer reaction. The differences in the electron-transfer mechanism and dynamics compared to Cyt-c are obviously related to the unique structural properties of Cyt-c(552) which may be the consequence of the adaptation to the extreme living conditions of the thermophilic bacterium.