Long-Range Electron Transfer in Heme Proteins

Abstract

Kinetic experiments have conclusively shown that electron transfer can take place over large distances (greater than 10 angstroms) through protein interiors. Current research focuses on the elucidation of the factors that determine the rates of long-range electron-transfer reactions in modified proteins and protein complexes. Factors receiving experimental and theoretical attention include the donor-acceptor distance, changes in geometry of the donor and acceptor upon electron transfer, and the thermodynamic driving force. Recent experimental work on heme proteins indicates that the electron-transfer rate falls off exponentially with donor-acceptor distance at long range. The rate is greatly enhanced in proteins in which the structural changes accompanying electron transfer are very small.

Nanosecond electron tunneling between the hemes in cytochrome bo 3

“…This treatment is based on theoretical (30) and experimental (31)(32)(33)(34) work that elucidated the free energy, temperature, and distance dependences of eT rates, with the nuclear term taken from classical Marcus theory (35). A correction term assumes nuclear tunneling with a single generic characteristic frequency to account for quantum effects (30,36), which is necessary because the high-temperature regime does not apply.…”

Reaction of Human Myoglobin and H2O2

“…In the human protein, however, the sulfhydryl group of Cys 110 is expected to be ϳ9 -10 Å from the heme edge, and the distance between the Cys 110 and Tyr 103 residues is ϳ12 Å (24 to the heme group. The relatively large distance separating the Tyr 103 and Cys 110 residues decreases the efficiency of intramolecular electron transfer between these residues, although long range intramolecular through-bond processes are known to occur in heme-proteins and therefore cannot be excluded (40). Interestingly, tyrosyl phenoxyl radicals (generated from reaction of horseradish peroxidase, H 2 O 2 , and free tyrosine) have been demonstrated to oxidize thiols to thiyl radicals by an intermolecular mechanism (41).…”

Ecoupling server: A tool to compute and analyze electronic couplings

“…This phenomenon is especially important to describe some mechanisms, as long-range ET where coupling though a bridge leads to a rapid ET [43][44][45][46] .…”