Tunneling pathway and redox-state-dependent electronic couplings at nearly fixed distance in electron transfer proteins

The tunneling pathway model for electron transfer, which accounts for the unique covalent, hydrogen-bonded, and van der Waals contact linking donor and acceptor in a protein, gives a consistent description of electron-transfer rates in ruthenated proteins (cytochrome c, myogloblin, and cytochrome b{sub 5}), while simpler exponential decay models are not fully adequate. The authors report several new testable predictions of the pathway model relating electron-transfer rates to protein structure. The analysis predicts qualitative differences in the distance dependence of protein electron transfer at short (