Redox thermodynamics of mutant forms of the rubredoxin from Clostridiumpasteurianum: Identification of a stable FeIII(S-Cys)3(OH) centre in the C6S mutant

Abstract

Redox thermodynamic data provide a detailed insight into control of the reduction potential E°′ of the [Fe(S-Cys)4] site in rubredoxin. Mutant forms were studied in which specific structural changes were made in both the primary and secondary coordination spheres. Those changes have been probed by resonance Raman spectroscopy. The decrease of ∼-200 mV in E°′ observed for the [Fe(S-Cys)3(O-Ser)]-/2- couples in the surface ligand mutants C9S and C42S is essentially enthalpic in origin and associated with the substitution of ligand thiolate by ligand olate. However, the pH dependence of the potentials below characteristic pKared≈7 is an entropic contribution, plausibly associated with increased..