TABLE I.

Rate constants and activation parameters for heme and hemin transfer from holoShp to apoHtsA

Kinetic parameter	Heme	Hemin
$\frac{k_2}{k_1}$ or Kda	120 ± 18 μM	48 ± 7 μM
ktransfera	28 ± 6 s−1	43 ± 3 s−1
ΔH°complexb	−77 ± 9 kJ/mol	−37 ± 6 kJ/mol
ΔS°complexb	−182 ± 30 J/mol-K	−37 ± 18 J/mol-K
ΔG°complexb	−23 kJ/mol	−26 kJ/mol
ΔS≠ for ktransferc	250 ± 25 J/(Kmol)	35 ± 4 J/(K·mol)
ΔH≠ for ktransferc	140 ± 13 kJ/mol	75 ± 9 kJ/mol
ΔG≠ for ktransferc	64.2 kJ/mol	64.9 kJ/mol
ktransfer/Kda, apparent bimolecular rate constant at low[Proteins],	0.3 μM−1s−1	0.8 μM−1s−1
kautox rate of Autooxidation of hemoHtsAd	0.017 ± 0.002 s−1

^aThe values for k₂/k₁ and k_transfer at 25° in 20 mM Tris-HCl at pH 8.0 were obtained from fits of the dependence of the observed rates of transfer on [apoHtsA] to Equation 1.

^bThe standard entropy, enthalpy, and free energy for the formation of the holoShp:apoHtsA complexes were obtained by analyzing the dependence of K_association (1/K_d) on temperature according to the van’t Hoff plot.

^cThe activation entropy, enthalpy, and free energy were obtained by analyzing the dependence of k_transfer on temperature according to the Eyring equation.

^dThe rate of autooxidation of hemoHtsA was obtained from the slow phase following heme transfer.