Electron transfer (ET) reactions are key steps in various biological processes such as photosynthesis and respiration . One finds many examples of protein networks consisting of Tyr and Trp residues in branched chains in ; the path of electron flow leads from a high potential heme active site through various residues at fixed potential, and terminates at a lowest potential residue situated at the exterior of the protein. A computer implementation of an ET network in generic form first appears in where the matrix exponential solver is used to provide concentration-time solutions to arbitrary first-order chemical reaction networks, one of which is an ET network.