INFLUENCE OF SURFACE-CHARGES ON REDOX PROPERTIES IN HIGH-POTENTIAL IRON-SULFUR PROTEINS

The pH-dependence of the reduction potential determined through differ ential pulse voltammetry for the high potential iron sulfur proteins ( HiPIP) from R. globiformis, C. vinosum, R. gelatinosus, E. vacuolata ( I and II), E. halophila (I and II) is reported. A decrease in reductio n potential with pH is invariably observed in the pH range where depro tonation of the imidazolium nitrogen of histidine residue(s) occurs. N o pH dependence is observed for the only protein lacking histidines. I t appears that surface charges like the His imidazolium groups are cap able of influencing the reduction potential despite the known quencing of the electrostatic interactions due to solvent effects. (C) 1994 Ac ademic Press, Inc.