The Ionisation Energy Term, IE

Mutant forms of RdCp have been generated with the aim of replacing each of the four cysteine ligands, in turn, by serine. These four proteins, C6S, C9S, C39S and C42S, would constitute four geometric isomers in which FeOS3 centres are 

The data are relative to those of the recombinant form, averaged in the range pH 6-10 

Enthalpic and entropic contributions to AE° (see Equation 2). Differences of 50 mV are considered to be significant 

Relative changes at pH values below the of the single mutant proteins 

The more positive reduction potential for C6S relative to those of C9S and C42S is then attributable to the presence of a less-electron-donating HO ligand relative to Ser-0 . 

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