Electron transfer in cytochrome c depends upon the structure of the intervening medium

Guidelines for tunneling in enzymes

“…Here again it appears that equation 1 gives rates consistent with observation when using the ruthenium to heme conjugated edge distance, especially when taking into account the mobility of certain of these ruthenium labels [32, 36]. Figure 2 shows that the free energy optimized rates for electron tunneling for myoglobin (circles) [10, 37, 38], cytochrome c (diamonds) [36, 37, 39-45], cytochrome b 5 (star) [46, 47] and cytochrome b 562 (squares) [36] fall in line with analogous rates found in the photosynthetic reaction centers (open circles) [2] when using a heme conjugated edge definition. This is the case even when the ruthenium center geometry places it either in approximately in the same plane as the heme, where the metal to conjugated edge distance is much different from the metal to metal distance, or approximately normal to the plane, where there metal to metal and metal to conjugated edge distances are similar.…”

Electron Tunneling in Proteins: Coupling Through a β Strand

“…is nearly equal to the estimated reorganization energy for this system (X -0.8 eV) (14); the observed rates are within 5% of the activationless rates (kmax). A plot of log kmax versus RM [RM, metal-metal separation (15)] for Ru-modified azurin is nearly linear (Fig.…”

“…We measured ET rates in eight different Ru(bpy)2(im)(HisX)-modified cytochromes c (cyt c) (8,14). However, in contrast to the case with Ru-modified azurin, there is no uniform secondary structure type separating the heme and the seven Ru-binding sites (Fig.…”

Comparison of theory and experiment for electron transfers in proteins: where's the beef?

“…In discussing the comparison of theory with experiment, I will focus principally on the studies by Gray and co-workers, including their paper in this issue of Structure [15]. Whereas a number of systems have been studied experimentally, it is Gray and co-workers who have provided the most extensive comparisons of theory with experiment in their studies of several proteins, particularly cytochrome c and myoglobin, after they have been chemically modified by the addition of a ruthenium compound that serves as a redox partner to the porphyrin chromophore already bound to the protein [15][16][17][18][19].…”