Calorimetric studies on the interaction of horse ferricytochrome c and yeast cytochrome c peroxidase

Abstract

The binding of horse ferricytochrome c to yeast cytochrome c peroxidase at pH 6.0 in 8.7 mM phosphate buffer (0.0100 M ionic strength) is characterized by a small, unfavorable enthalpy change (+1.91 +/- 0.16 kcal mol-1) and a large, positive entropy change (+37 +/- 1 eu). The free energy of binding depends strongly upon ionic strength, increasing from -9.01 to -4.51 kcal mol-1 between 0.0100 and 0.200 M ionic strength. The increase in free energy is due solely to the change in entropy over this ionic strength range, with the entropy change decreasing from 37 +/- 1 to 22 +/- 3 eu between 0.0100 and 0.200 M ionic strength. The observed enthalpy change remains constant over the same ionic strength range. At 0.0100 M ionic strength, complex formation is accompanied by the release of 0.54 +/- 0.11 proton, causing a variation in the observed enthalpy of reaction depending upon the buffer. After accounting for proton binding to the buffer, the corrected values for the enthalpy and entropy of binding are +2.84 +/- 0.26 kcal mol-1 and +21 +/- 3 eu, respectively. At 0.05 M ionic strength, the observed change in heat capacity, delta Cp, for the reaction between horse ferricytochrome c and cytochrome c peroxidase is essentially zero, 1.6 +/- 9.6 cal mol-1 K-1. The corrected delta Cp for binding is -28 +/- 10 cal mol-1 K-1 after accounting for proton binding to the buffer. No evidence for formation of a 2:1 horse ferricytochrome c/cytochrome c peroxidase complex was obtained in this study.

Coarse-grained Models for Simulations of Multiprotein Complexes: Application to Ubiquitin Binding

“…As shown in Table 2, the estimated binding affinities for models B (620 μM) and C (850 μM) at 150 mM salt concentration are in agreement with experimental values, K d ≃ 100 μM and K d ≃ 300 to 1000 μM at 100 and 200 mM salt concentrations, respectively. 45,46 For the other models, the Cc/CcP complex exhibits weaker affinities between 1.5 and 2.0 mM (Fig. 2).…”

The Role of Water Molecules in the Association of Cytochrome P450cam with Putidaredoxin

“…Correlation of a process with osmotic pressure implies a change in the size of this population. Previous studies have shown that most protein-protein association processes in the ET reactions are usually accompanied by the release of water molecules from the interface of the complex through the hydrophobic interactions (12,(33)(34)(35)(36). The increase of osmotic pressure leads to the increase of its association constants because of the desolvation at the complex interface, as seen in the cytochrome b 5 -cytochrome c association reaction (⌬V W ϭ Ϫ47 cm 3 /mol) (34).…”

The Salt-dependence of a Protein–Ligand Interaction: Ion–Protein Binding Energetics

“…[2][3][4][5][6] They perform less well when applied to small molecule-protein interactions, and in cases where a strong salt-dependence is observed. 7 The parameters used in calculating the enthalpy of an interaction based on surface area are derived from protein unfolding data 3,5,8 or energetics of transfer of amide and hydrocarbon compounds from dilute aqueous solution to pure liquid. 9 In both cases, charge transfer from one environment to another is under-represented in the data sets used for the parameterization.…”