Thermodynamical properties of reaction intermediates during apoplastocyanin folding in time domain.

Two intermediates observed for the folding process of apoplastocyanin (apoPC) were investigated by using a photoinduced triggering system combined with the transient grating and transient lens methods. The thermodynamic quantities, enthalpy, heat capacity, partial volume, and thermal expansion volume changes during the protein folding reaction were measured in time domain for the first time. An interesting observation is the positive enthalpy changes during the folding process. This positive enthalpy change must be compensated by positive entropy changes, which could be originated from the dehydration effect of hydrophobic residues and/or the translational entropy gain of bulk water molecules. Observed negative heat capacity change was explained by the dehydration effect of hydrophilic residues and/or motional confinement of amino acid side chains and water molecules in apoPC. The signs of the volume change and thermal expansion volume were different for two processes and these changes were interpreted in...