Table 2.
(A) Calorimetric enthalpy calculated from thermal unfolding experiments (Fig. 5) using differential scanning calorimetry. Conditions: 5 μM human myeloperoxidase in 5 mM phosphate buffer, pH 7.0. (Native enzyme or incubated with 100- or 1000-fold stoichiometric amount of hydrogen peroxide for 2 h. (B) Thermodynamic data of thermal unfolding (calculated from van’t Hoff plot) for MPO without and with 100 and 1000 fold excess of H2O2 followed by electronic circular dichroism spectroscopy at 222 nm.
| MPO | MPO plus 100 eq H2O2 |
MPO plus 1000 eq H2O2 |
|
|---|---|---|---|
| (A) | |||
| ΔHm (kJ mol−1) | – | – | 38.5 |
| ΔHm2 (kJ mol−1) | 111.7 | 104.6 | 85.0 |
| ΔHm3 (kJ mol−1) | 138.7 | 135.0 | 140.3 |
| ∑ΔHm (kJ mol−1) | 250.5 | 239.6 | 263.8 |
| MPO ([θ]222) | MPO 100 eq H2O2 ([θ]222) | MPO 1000 eq H2O2 ([θ]222) | |
| (B) | |||
| Tm (°C) | 76.8 ± 0.1 | 76.1 ± 0.2 | 73.2 ± 0.1 |
| ΔHm (kJ mol-1) | 261.4 ± 16.7 | 245.7 ± 18.9 | 266.7 ± 11.5 |
| ΔSm (J mol-1) | 746.8 ± 48.7 | 703.6 ± 54.3 | 770.1 ± 33.2 |
| ΔCp (kJ mol-1 K-1) | 4.88 | 4.70 | 5.41 |
| ΔG25°C (kJ mol-1) | 18.9 | 17.4 | 17.6 |