Electron flow through proteins

Biol. electron transfers often occur between metal-contg. cofactors that are sepd. by very large mol. distances. Understanding the underlying physics and chem. of these electron transfer processes is the goal of much of the work in my lab. Employing laser flash-quench triggering methods, my coworkers and I have shown that 2-nm, coupling-limited Fe(II) to Ru(III) and Cu(I) to Ru(III) electron tunneling reactions in Ru-modified cytochromes and blue copper proteins occur on microsecond to nanosecond timescales. Redox equiv. can be transferred even longer distances by multistep tunneling (called hopping) through intervening tyrosines and tryptophans: notably, in our work on cytochrome P 450 and azurin, we have found that long-range hole hopping through intervening tryptophans can be orders of magnitude faster than single-step tunneling. Water interactions with tryptophan radical cation intermediates play key roles in promoting these hole hopping processes.