Reversible unfolding of poplar iso-plastocyanins

We attempted to determine the experimental conditions under which poplar plastocyanin iso-forms PCa and PCb undergo reversible thermal unfolding studied by differential scanning calorimetry (DSC). Our results indicate that an exothermic unfolding process exists always in the presence of molecular oxygen. Reversible unfolding and almost perfect two-state transitions were exhibited in the presence of TCEP under anaerobic conditions. This suggests that the second endothermic peak is due to copper-site disulfide dimmers formed during thermal denaturation. The conformational thermal stability of reduced PCb (ΔG (25 °C) = 33.9 kJ mol⁻¹) has proven to be higher than that of reduced PCa (ΔG(25 °C) = 22.9 kJ mol⁻¹).