The long term goal of this work is to delineate the factors which control electron transfer in biological systems specifically in cytochromes c and b5. (1) The role of protein surface charges will be evaluated by studying cytochromes with altered electrostatic surfaces. (2) The rate constant for electron transfer is thought to decrease exponentially with distance; this distance dependence may in turn be a function of the driving force for the reaction. Dr. Dixon will make a series of cytochromes b5. with increasing steric bulk at the electron transfer site. Rate constants at different driving forces will be measured. The resulting matrix of rate constants will be used to assess the dependence of electron transfer on distance and driving force. (3) Dr. Dixon will use NMR techniques to measure both electron transfer rate constants and protein motions for a series of cytochromes c in an effect to understand the molecular basis of conformational and reorganizational control of electron transfer. Particular emphasis will be placed on the structure of cytochrome c as a function of ionic strength, on the kinetics of the reversible loss of the axial methionine and on the roles of residues near the heme in controlling electron transfer.
