Table 4.

Reduction Potentials and Calculated Energy Differences at pH 7.4 for Yeast iso-1 Cytochrome c Variants

Variant	Reduction potential (mV vs SHE)				Calculated ΔΔG (kJ/mol)
	$E_{\text{Met}*}^{{°}^{\prime }}$a	$E_{{\text{Met|TH}}^{+}}^{{°}^{\prime }}$b	$E_{\text{Met|TH}}^{{°}^{\prime }}$b	$E_{\text{Lys}}^{{°}^{\prime }}$a	$\Delta G_{\text{Met}-\text{Fe}(\text{II})}^{{\circ }^{\prime }}-\Delta G_{\text{Met}-\text{Fe}(\text{III})}^{{\circ }^{\prime }}$c	$\Delta G_{\text{Lys}-\text{Fe}(\text{II})}^{{\circ }^{\prime }}-\Delta G_{\text{Lys}-\text{Fe}(\text{III})}^{{\circ }^{\prime }}$c	$\Delta G_{\text{Met}-\text{Fe}(\text{II})}^{{\circ }^{\prime }}-\Delta G_{\text{Lys}-\text{Fe}(\text{III})}^{{\circ }^{\prime }}$d
K79G	262±3	265±38	148±36	−145±10e	−25.6±3.7	14.0±1.0	−32.4±3.9
T49V/K79G	197±4	201±28	48±25	−141±10	−19.4±2.7	13.6± 1.0	−15.4±2.9
T78V/K79G	275±3	277±45	184±38	−140±4	−26.7±4.3	13.5±0.4	−22.7±4.5

^aExperimental values measured at scan rates 20 V/s.

^bCalculated values according to Scheme 1.

^cCalculated from the reduction potentials of the Met-Fe|TH⁺ or Lys-Fe|T species by $\Delta \Delta G=-\text{nF}{E}_{\text{Met}|{\text{TH}}^{+}}^{{\circ }^{\prime }}$ or $\Delta \Delta G=-\text{nF}{E}_{\text{Lys}}^{{\circ }^{\prime }}$.

^dCalculated according to Scheme S2, where the diagonal $\Delta G_{\text{Met}-\text{Fe}(\text{II}){\text{TH}}^{+}}^{°\prime }-\Delta G_{\text{Lys}-\text{Fe}(\text{III})\text{T}}^{{°}^{\prime }}=-\text{nF}{E}_{\text{Met}|{\text{TH}}^{+}}^{*}+\text{RTln}{K}_{\text{eq}}{}^{\text{III}}$. K_eq^III is a pH-adjusted equilibrium constant between the Lys-Fe(III)|T and Met-Fe(III)|TH⁺ species and is determined by $K_{\text{eq}}^{\text{III}}={10}^{\text{pH-}{K}_{\text{a}}^{\text{III}}}$.

^eThe reduction potential of Lys-ligated K79G was measured at pH 10, while the other $E_{\text{Lys}}^{{°}^{\prime }}$ potentials and all of the $E_{\text{Met}*}^{{°}^{\prime }}$ potentials were measured at pH 7.4.