Robust Electron Transfer Protein Design

CHAINS AND ROBUST ELECTRON TRANSFER PROTEIN DESIGN 

To transfer electrons over extended distances between catalytic sites of substrate oxidation and reduction and sites of energy conversion. Nature relies on redox chains. The use of chains allows biological electron transfer to escape the exponential decrease of rate with distance, and to recover an essentially linear dependence of rate over very long distances, keeping tunneling rates faster than the kcat of the enzymes. 

Chains also contribute to the robustness of natural electron transfer protein design because the close spacing between successive redox centers means that the driving force of the reaction can usually vary widely with relatively little effect on the overall electron transfer rate through the protein. Indeed, many naturally occurring chains have uphill electron transfer steps of hundreds of meV. 

FIGURE 7. Two redox cofactor chains meet at the bacteriochlorophyl dimer in the photosynthetic reaction center of Rp. viridis. Electron transfer takes place by tunneling between cofactors diat are spaced by no more dian 14, assuring overall elech on transfer rates in the msec or faster range, even though a total distance of 70 is crossed by the c heme chain. 

Equations 10 and 11 perform quite well in estimating rates of electron transfer chains, for example, in the experimentally reported rates for several 

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