期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2005
卷号：102
期号：31
页码：10882-10886
DOI：10.1073/pnas.0503001102
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Electron transfer (ET) within proteins occurs by means of chains of redox intermediates that favor directional and efficient electron delivery to an acceptor. Individual ET steps are energetically characterized by the electronic coupling V, driving force {Delta}G, and reorganization energy {lambda}. {lambda} reflects the nuclear rearrangement of the redox partners and their environment associated with the reactions; {lambda} {approx} 700-1,100 meV (1 eV = 1.602 x 10-19 J) has been considered as a typical value for intraprotein ET. In nonphotosynthetic systems, functional ET is difficult to assess directly. However, using femtosecond flash photolysis of the CO-poised membrane protein cytochrome c oxidase, the intrinsic rate constant of the low-{Delta}G electron injection from heme a into the heme a3-CuB active site was recently established at (1.4 ns)-1. Here, we determine the temperature dependence of both the rate constant and {Delta}G of this reaction and establish that this reaction is activationless. Using a quantum mechanical form of nonadiabatic ET theory and common assumptions for the coupled vibrational modes, we deduce that {lambda} is <200 meV. It is demonstrated that the previously accepted value of 760 meV actually originates from the temperature dependence of CuB-CO bond breaking. We discuss that low-{Delta}G, low-{lambda} reactions are common for efficiently channeling electrons through chains that are buried inside membrane proteins.
关键词：reorganization energy ; ultrafast spectroscopy ; CuB–CO bond ; electron transfer
