Gray H B, Malmström B G, Williams R J
California Institute of Technology, Beckman Institute, Pasadena 91125, USA.
J Biol Inorg Chem. 2000 Oct;5(5):551-9. doi: 10.1007/s007750000146.
The spectroscopic and electrochemical properties of blue copper proteins are strikingly different from those of inorganic copper complexes in aqueous solution. Over three decades ago this unusual behavior was ascribed to constrained coordination in the folded protein; consistent with this view, crystal structure determinations of blue proteins have demonstrated that the ligand positions are essentially unchanged on reduction as well as in the apoprotein. Blue copper reduction potentials are tuned to match the particular function of a given protein by exclusion of water from the metal site and strict control of the positions of axial ligands in the folded structure. Extensive experimental work has established that the reorganization energy of a prototypal protein, Pseudomonas aeruginosa azurin, is approximately 0.7 eV, a value that is much lower than those of inorganic copper complexes in aqueous solution. The lowered reorganization energy in the protein, which is attributable to constrained coordination, is critically important for function, since the driving forces for electron transfer often are low (approximately 0.1 eV) between blue copper centers and distant (>10 A) donors and acceptors.
蓝色铜蛋白的光谱和电化学性质与水溶液中的无机铜配合物显著不同。三十多年前，这种异常行为被归因于折叠蛋白中受限的配位；与此观点一致，蓝色蛋白的晶体结构测定表明，配体位置在还原以及脱辅基蛋白中基本不变。通过将水排除在金属位点之外，并严格控制折叠结构中轴向配体的位置，蓝色铜的还原电位被调整以匹配特定蛋白质的特定功能。大量实验工作已经确定，一种典型蛋白质——铜绿假单胞菌天青蛋白的重组能约为0.7电子伏特，该值远低于水溶液中无机铜配合物的重组能。蛋白质中重组能的降低归因于受限的配位，这对功能至关重要，因为蓝色铜中心与远处（>10埃）供体和受体之间的电子转移驱动力通常很低（约0.1电子伏特）。
