PROTEIN ELECTRON-TRANSPORT - SINGLE VERSUS MULTIPLE PATHWAYS

Pathway analysis provides a tool for the design of tailored electron-transfer proteins and is a useful starting point from which to build up multipathway views of electron mediation that include the influence of interference and all of the chemical tunability that is accessible. We present a new theoretical strategy to determine when a single-pathway picture is sufficient or when one must consider multiple paths. A definition of a single pathway in the context of a Green's function formalism is presented. To illustrate these effects, examples are given for cytochrome c. We also show that full protein Green's function calculations can be carried out at the tight-binding (extended-Huckel) level on cytochrome c including all valence orbitals of the protein. Although many questions remain about appropriate parameterization, the simple Pathway prediction that proteins are not structureless isotropic electron-transfer barriers holds as multiple pathways are included in the calculations and backscattering of electron amplitude within and between pathways is added.