ELECTRON-TRANSFER IN PROTEINS

The past year has seen significant advances in our understanding of electron transfer (ET) events in biological and synthetic protein systems. Experiment and theory have begun to merge towards a more complete picture of the role that protein plays in mediating ET reactions. This review highlights these developments and discusses the roles played by distance, protein medium, driving force, and reorganization energy in controlling ET rates in natural and artificial systems. These parameters, drawn from ET theory, are discussed in terms of their natural selection to govern biological ET. We find that distance, driving force, and reorganization energy are the main determinants of ET rates and directional specificity. Another parameter that can have significant effects on rates over physiological distances is the structure of the intervening medium between the electron donor and acceptor cofactors. There is nevertheless no clear evidence that the effect of distance on ET is modified by the intervening protein structure so as to favor productive forward ETs over energy-wasting reverse reactions in key biological ET systems.