Long-range electron transfer azurin systems

Direct evidence for long range electron-transfer in biological systems was first observed by Gray et al.50,51) and Isied et al.481 using [Ru(NH3)5]3+ substituted metallo protein. Histidine-83 of blue copper (azurin) was labeled with Ru(III)(NH3)5 50). Flash photolysis reduction of the His-83 bound Ru(III) followed by electron-transfer from the Ru(II) to Cu2+ was observed with a rate constant of 1.9 s 1. The result shows that intramolecular long distance (approx. 1 nm) electron-transfer from the Ru(II) to the Cu2 + of the azurin takes place rapidly. 

Some of the first protein systems where pulse radiolysis was used to help determine mechanism were those of blue copper proteins. These are proteins that are blue in solution and contain what are known as type (I) and type (2) copper centers. Two of the most well-known and well-characterized examples of these are azurin and cytochrome c. It was the studies of these systems that opened up the field of long-distance electron transfer in proteins and, by using the protein structure as a framework for electron transfer through space and through bonds, allowed for the development of a broad theoretical basis and many fascinating experiments on long-range electron transfer. Here, I will limit the discussion to electron transfer studies in azurin as illuminated by pulse radiolysis studies. ... 

Jensen, P.S., Chi, Q., Zhang, J., and Ulstrup, J. (2009) Long-range interfadal electrochemical electron transfer of Pseudomonas aeruginosa azurin-gold nanoparticle hybrid systems. Journal of Physical Chemistry C, 113,13993-14000. 

Electron transfer in biological systems where the electron donor and acceptor are separated by a long molecular distance is encountered in very important processes such as photosynthesis and respiration [54]. As natural systems are not appropriate for such studies. Gray et al. have employed proteins chemically labeled with transition metal complexes to measure ET rates in metaUoproteins. In particular, they have shown that long-lived luminescent probes enabled a wider range of ET measurements than is possible with non-luminescent complexes [55]. The blue copper protein azurin is a convenient model for the study of ET in p-sheet proteins. 

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