EFFECT OF VISCOSITY ON INTRAMOLECULAR ELECTRON TRANSFER IN SULFITE OXIDASE

Rohit Kedia1, Changjian Feng1, James T. Hazzard2, Gordon Tollin2, and John H. Enemark1. (1) Department of Chemistry, University of Arizona, Tucson, AZ 85721, rvkedia@u.arizona.edu, (2) Department of Biochemistry, University of Arizona

Our previous studies have shown that the rate of intramolecular electrontransfer (IET) between the heme and molybdenum centers of sulfite oxidase varies from about 20-1500 s-1. These two centers are linked by a flexible polypeptide loop, suggesting that conformational changes that alter the Mo...Fe distance play an important role in the observed IET rates. This investigation shows that the rate constant for IET, kobs (kobs=kforward + kreverse), is inversely proportional to solvent viscosity. The marked dependence of the individual rate constants kforward and kreverse on viscosity is consistent with the suggestion that conformational changes of sulfite oxidase play an important role in the observed rates of IET. The viscosity dependence of the steady-state kinetics of sulfite oxidase will also be presented.