Abstract

From 0 to 8 redox cofactors lie between substrate binding sites in natural oxidoreductases; often these cofactors form a line through the protein. For more than 30 physiologically relevant intraprotein electron transfers of different types, the distances between edges of the redox partners uniformly fall between 4.0 and 13.5 Å. It appears that this close proximity of donor and acceptor precludes or diminishes evolutionary pressure for highly connected bonding protein motifs to promote simple electron tunneling between cofactors; continued careful analysis is needed to confirm this view. Proximity in the individual steps of electron transfer may also eliminate the need to utilize large driving forces (i.e., negative ΔG°) to achieve high rates. Indeed, we find that the large majority of –ΔG° values of the individual steps in redox chains involving simple electron transfer are within 100 mV of zero (many are even endrothermic) and art far from reorganization energy value (λ) needed for optimized rates.

© 1997 Optical Society of America