Abstract
The effect of pressure on the unfolding of the native (N) and molten globule (MG) state of canine milk lysozyme (CML) was examined using ultraviolet (UV) spectroscopy at pH 4.5 and 2.0, respectively. It appeared that the thermally induced unfolding was promoted by the increase of pressure from atmospheric to 100 MPa, which indicates that both the N and MG states of CML unfolded with the decrease of the partial molar volume change (Δ V). The volume changes needed for unfolding were estimated from the free energy change vs. pressure plots, and these volume changes became less negative from 20 to 60 °C. The Δ V values at 25 °C were obtained for the N–MG (−46 cm 3/mol) and MG-unfolded-state (U) transition (−40 cm 3/mol). With regards to the MG–U transition, this value is contrastive to that of bovine α-lactalbumin (BLA) (0.9 cm 3/mol), which is homologous to CML. Previous studies revealed that the MG state of CML was significantly more stable, and closer to the N state in structure, than that of BLA. In contrast to the swollen hydrophobic core of the MG state of BLA, our results suggest that the MG state of CML possesses a tightly packed hydrophobic core into which water molecules cannot penetrate.
Published Version
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