Electron tunneling through proteins


HB. Gray, hbgray@caltech.edu, Beckman Institutue, California Institute of Technology, Pasadena, CA 91125 and J. R. Winkler, Beckman Institute, California Institute of Technology, Pasadena, CA 91125.
Understanding the underlying physics and chemistry of biological electron transfer processes is the goal of much of the work in our laboratory. Employing laser flash/quench triggering methods, we have shown that 20-angstrom, coupling-limited Fe(II) to Ru(III) and Cu(I) to Ru(III) electron tunneling in Ru-modified iron and copper proteins can occur on the microsecond timescale both in solutions and crystals; and, further, that analysis of these rates suggests that distant donor-acceptor electronic couplings are mediated by a combination of sigma and hydrogen bonds in folded polypeptide structures. In recent work, we have found that 20-angstrom hole hopping through intervening tryptophan residues is several hundred-fold faster than single-step electron tunneling in Re-modified copper proteins. Lessons learned about the control of electron tunneling and hopping are now being used to design sensitizer-modified protein machines incorporating catalysts that can generate hydrogen fuel from sunlight and water.