A tubular view of electron transfer in azurin

A new theoretical approach emphasizes tubes (tightly grouped families of pathways) for electron transfer and looks for interaction between these families rather than focussing on individual paths. in some cases, for a given donor D and acceptor A, the electron transfer can be thought of as pathway-like wherein the protein bridge can be physically reduced to a tube without changing the overall coupling. In other cases, the transfer is characterized by multiple tubes which can interfere with one another, and a single path assumption will fail to identify all of the structural elements which control the coupling. Reducing the protein to only the relevant parts (tubes) that mediate the tunneling matrix element is a useful tool for understanding electron transfer in biological medium. An example is carried out on blue copper protein azurin that plays an important role as an electron carrier in biological systems. (N.T.)