Electron tunneling through proteins

Abstract

Electron transfer processes are vital elements of energy transduction pathways in living cells. More than a half century of research has produced a remarkably detailed understanding of the factors that regulate these 'currents of life'. We review investigations of Ru-modified proteins that have delineated the distance- and driving-force dependences of intra-protein electron-transfer rates. We also discuss electron transfer across protein-protein interfaces that has been probed both in solution and in structurally characterized crystals. It is now clear that electrons tunnel between sites in biological redox chains, and that protein structures tune thermodynamic properties and electronic coupling interactions to facilitate these reactions. Our work has produced an experimentally validated timetable for electron tunneling across specified distances in proteins. Many electron tunneling rates in cytochrome c oxidase and photosynthetic reaction centers agree well with timetable predictions, indicating that the natural reactions are highly optimized, both in terms of thermodynamics and electronic coupling. The rates of some reactions, however, significantly exceed timetable predictions: it is likely that multistep tunneling is responsible for these anomalously rapid charge transfer events.

Measurement of the Heme Affinity for Yeast Dap1p, and Its Importance in Cellular Function

“…This value is in the range of cytochrome P 450 reductases,(34) making it tempting to suggest that Dap1p could provide electrons to Erg11p and hence increase the Erg11p activity in the cell with Dap1p present, as suggested by Hughes et al (8). However, this hypothesis is unlikely since typical electron transport proteins, such as cytochrome b5, have similar coordination environments between their biologically relevant oxidation states (35). In addition, since the ferrous heme does not bind well to Dap1p, the heme would likely dissociate during redox catalysis (35).…”

“…However, this hypothesis is unlikely since typical electron transport proteins, such as cytochrome b5, have similar coordination environments between their biologically relevant oxidation states (35). In addition, since the ferrous heme does not bind well to Dap1p, the heme would likely dissociate during redox catalysis (35). Finally, attempts to reduce the rat Dap1p homologue, IZA, by P 450 reductases and cytochrome b 5 have been unsuccessful in vitro (9).…”

Photoassembly of the water-oxidizing complex in photosystem II

“…The thermodynamic efficiency of this chemistry has never been replicated in any abiotic catalyst of any kind. Unlike the reasonably well understood principles of single-electron and single-proton transfer chemistry, complex multi-electron/proton reactions control the overall energetics and thus the allowed pathway for catalysis [8,9,10]. Interested readers should also consult other recent reviews that cover in vitro and in vivo photoactivation of the WOC [11,12,13].…”

A critical assessment of the information processing capabilities of neuronal microtubules using coherent excitations

“…This residue could be capable of supplying a mobile electron to the doublewell structure for use in electron transfer processes. At physiological energies, long-range electron tunneling appears to be viable mechanism for standard electron transfer in proteins [42], with consecutive electron tunneling jumps occurring between specific redox sites or protein-bound cofactors [43,44]. Typically, distances range between 10 and 15 Å [45,46] with the interaction greatly diminished with distances greater than l0 Å [47].…”