Abstract
Analysis of electron-transfer (ET) kinetics data obtained from experiments on Ru-modified proteins (cytochrome c, azurin, myoglobin) reveals that distant donor-acceptor electronic couplings depend upon the secondary structure of the intervening polypeptide matrix. Rates of Fe2+→Ru3+ ET reactions in cytochrome c decay exponentially with tunneling-pathway length (decay constant 0.73 A–1); these rates also decay exponentially with Ru-Fe distance (decay constant 1.1 A–1). In azurin, a β-sheet protein, Cu+→Ru3+ rates exhibit an exponential Cu-Ru distance dependence with a decay constant of 1.1 A–1. Comparison of distant couplings in azurin and myoglobin suggests that hydrogen bonds are better mediators across β sheets than through α helices.
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