Introduction

Protein electron transfer (ET) reactions are central to biological function. They are important components of bioenergetic pathways (photosynthesis and respiration) and they are involved in biological signalling and in the generation and the control of disease (Marcus and Sutin, 1985; Bendall, 1996; Canters and Vijgenboom, 1997; Page et al., 1999; Blankenship, 2002; Gray and Winkler, 2003, 2005). For a fundamental understanding of these biological processes it is necessary to study protein ET mechanisms at the molecular level. Protein ET physics is very rich because it involves charge transport through dynamic and responsive (to the transferring charge) molecular media organized in cellular molecular assemblies. A common feature among protein ET assemblies is that they are designed to move electrons to specific locations along transport pathways that partially suppress backward ET (Figure 9.1). In many cases the structures and dynamics of the protein ET complexes are such that ET takes place with high efficiency (Blankenship, 2002). Needless to say, an understanding of structural and dynamical effects on protein ET processes is very important for the development of new biomimetic electronic and energy-conversion materials with controlled functionalities (Jortner and Ratner, 1997; Balzani et al., 2001; Adams et al., 2003; Blankenship et al., 2011). The field of biological ET (and in particular protein ET) is one of the oldest fields in molecular biophysics (Marcus and Sutin, 1985; Bendall, 1996; Page et al., 1999; Jortner and Bixon, 1999; Kuznetsov and Ulstrup, 1999; May and Kühn, 2011; Balzani et al., 2001; Blankenship, 2002; Gray and Winkler, 2003, 2005; Nitzan, 2006).