Thermochemical, Volumetric and spectroscopic properties of lysozyme-poly(ethylene) glycol system

Investigations of lysozyme-polyethylene glycol system were made by differential scanning calorimetry, fluorescence and density techniques. The values of unfolding enthalpies, ?H NU, unfolding temperatures, T m, excess molar heat capacities, ?C p, and apparent molar volumes, V ? , were determined as functions of PEG concentration. The three PEGs of average molecular mass (MW) 6000, 10000, 20000 were used as macromolecular crowding agents. The concentration of polymers was changed in the range 0-30% mass per volume (w/v). The values of ?H NU remained constant with no dependence on PEG concentration, while PEG addition to buffered lysozyme solutions caused linear decrease of T m. The values of ?C p and V ? of lysozyme dramatically changed in the range of 8-10% of PEG concentration. The fluorescence spectroscopy was used in order to investigate the polymer influence on possible solvent-lysozyme interactions. The electrical properties of polymer-water and polymer-buffer systems, the dielectric constants of solutions were determined with use of impedance spectroscopy. © 2006 Akadémiai Kiadó.