PROTEIN ELECTRON-TRANSPORT - SINGLE VERSUS MULTIPLE PATHWAYS

Pathway analysis provides a tool for the design of tailored electron-t ransfer proteins and is a useful starting point from which to build up multipathway views of electron mediation that include the influence o f interference and all of the chemical tunability that is accessible. We present a new theoretical strategy to determine when a single-pathw ay picture is sufficient or when one must consider multiple paths. A d efinition of a single pathway in the context of a Green's function for malism is presented. To illustrate these effects, examples are given f or cytochrome c. We also show that full protein Green's function calcu lations can be carried out at the tight-binding (extended-Huckel) leve l on cytochrome c including all valence orbitals of the protein. Altho ugh many questions remain about appropriate parameterization, the simp le Pathway prediction that proteins are not structureless isotropic el ectron-transfer barriers holds as multiple pathways are included in th e calculations and backscattering of electron amplitude within and bet ween pathways is added.