Interprotein Electron Transfer Reactions

The interprotein electron transfer reactions are much more complicated because they involve at least three steps ... 

Davidson VL. Unravehng the kinetic complexity of interprotein electron transfer reactions. Biochemistry 1996 36 14035-9. 

In a coupled electron transfer reaction, the preceding adiabatic reaction step influences the experimentally-determined rate constant even though the electron transfer step is the slowest for the overall redox reaction. This occurs when the relatively fast reaction step which precedes electron transfer is very unfavorable (i.e. Kx (kx/kfix) l)- In Hii case, ks will be influenced by the equilibrium constant for that non-electron transfer process such that ks = kgT Kx (Harris et ah, 1994 Davidson, 1996). It follows that the experimentally-derived X ( lobs) may contain contributions from both the electron transfer event and the preceding reaction step (i.e. obs [ ET. x])- For example, lo sfor interprotein electron transfer reactions may reflect contributions from an intracomplex rearrangement of proteins after binding to achieve an optimum orientation for electron transfer. As with a true electron transfer reaction, k3 will vary with AG° since ks is proportional to ksT, although H b may also be affected by the coupling. 

Bishop, G. R., and Davidson, V. L., 1997, Catalytic role of monovalent cations in the mechanism of proton transfer which gates an interprotein electron transfer reaction. Biochemistry 36 3586nl3592. 

The interprotein electron-transfer reactions of Ru-65-cyt bs can be studied using a sacrificial electron donor such as aniline to reduce Ru(III) and prevent the back reaction k2, as described in Scheme 2. Appropriate sacrificial electron donors can also reduce Ru(IB) to Ru(I), which then reduces Fe(III) as shown in the top pathway of Scheme 2. Cyt b is rapidly reduced by either pathway, and is then poised to transfer an electron to another protein. The reaction of cyt bs with Cc using this methodology will be described in the next section. Covalent labelling of Cc with ruthenium complexes and subsequent flash photolysis has provided a... 

Davidson VL. What controls the rates of interprotein electron transfer reactions. Acc. Chem. Res. 2000 33 87-93. 

Hitomi Y, Hayashi T, Wada K, Mizutani T, Hisaeda Y, Ogoshi H. Interprotein electron transfer reaction regulated by an artificial interface. Angew. Chem., Int. Ed. 2001 40 1098-1101. 

These intramolecular electron transfer processes provide an opportunity to examine electron transfer within the protein environment. Addition of a reduc-tant, such as aniline, results in efficient reaction of the Ru(III) with the reduc-tant to form Ru(II), which leaves the heme iron in the reduced state. If a redox active metalloprotein is present in the solution, electron transfer between the reduced heme and the added protein can be observed. Production of reduced heme iron and removal of the Ru(III) intermediate can be accomplished within a few hundred nanoseconds, which allows the study of extremely rapid interprotein electron transfer reactions. 

Miyashita O, Okamura MY, Onuchic JN. Interprotein electron transfer from c)4ochrome c(2) to photosynthetic reaction center Tunneling across an aqueous interface,Proc. Natl. Acad. Sci. U.S.A. 2005 102 3558-3563. 

Smface modification with ruthenium complexes has proven valuable in studies of both interprotein and intraprotein electron transfer in systems that are difflcult to stndy by traditional kinetic tools. The choice of ruthenium complexes in these investigations stems from an extensive photochemistry as well as exceptional thermal stability. The photochemistry provides a means of examining reactions over a time range of nanoseconds to seconds by laser-flash photolysis and the thermal stability allows researchers to covalently bind a wide variety of complexes to proteins with... 

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