The key to rapid, long-range movement of electrons through proteins is the strategic placement of redox-active intermediates between the origin and destination of the transferring charge. Gray provides an example of a peroxidase network in which a heme active site acting as a source delivers charge through a chain of tryptophan and tyrosine residues. The chain typically ends at a residue situated on the surface of the protein where the potential is known to be lower than the common potential of identical residues in the protein core. Of interest is the influence of the number of residues (i.e., relays) in a chain on the transport time of electrons leading from the heme to the surface. From these concepts was developed the following chain model of N relays (N = 1, 2, 3, . . . ).