THz absorption spectroscopy of solvated β-lactoglobulin.

The influence of β-lactoglobulin (βLG) on the fast sub-picosecond collective hydration dynamics in the solvent was investigated by THz absorption spectroscopy as a function of pH. It is well-known that a change in pH from pH 6 to pH 8 reversibly opens or closes the binding cavity by a transition of the E-F loop. Furthermore, the aggregation of the protein into dimers is affected, which is thought to be triggered by changes in the enzyme's electrostatic potential. Our data reveal that pH has a clear influence on the THz absorption of βLG. We discuss this influence in light of the changes observed in the sub-psec solute/solvent dynamics when probed by THz spectroscopy, which are, in turn, seen to correlate with changes in the pH value.