Redox thermodynamics of low-potential iron-sulfur proteins

The enthalpy and entropy changes associated with protein reduction (DeltaH degrees'(rc), DeltaS degrees'(rc)) were determined for a number of low-pote ntial iron-sulfur proteins through variable temperature direct electrochemi cal experiments. These data add to previous estimates making available, ove rall, the reduction thermodynamics for twenty species from various sources containing all the different types of metal centers. These parameters are d iscussed with reference to structural data and calculated electrostatic met al-environment interaction energies, and redox properties of model complexe s. This work, which is the first systematic investigation on the reduction thermodynamics of Fe-S proteins. contributes to the comprehension of the de terminants of the differences in reduction potential among different protei n families within a novel perspective. Moreover, comparison with analogous data obtained previously for electron transport (ET) metalloproteins with p ositive reduction potentials, i.e., cytochromes c, blue copper proteins, an d HiPIPs, helps our understanding of the factors controlling the reduction potential in ET species containing different metal cofactors. The main resu lts of this work can be summarized as follows.