| One of the keys to control protein activity and to improve bio-preservation for biological and pharmaceutical applications is to control the protein dynamics by changing the solvents. It still remains a challenge to understand the influence of solvents on protein dynamics. In this Dissertation, light and neutron-scattering data have been used to elucidate the protein dynamics that take place in the rather poorly investigated GHz ∼ THz frequency region. Interferometry has been used for the first time to observe the dynamics in this range. Light-scattering, compared to neutron-scattering, has proved to be a viable method of assessing the dynamic behavior of biological systems like proteins. The results on the model protein lysozyme in different solvent environments have been compared to data in the literature in an effort to establish a relationship between the relatively fast dynamics and longer time-scale bioactivities.; There are two main relaxation processes in the frequency window of interest: fast and slow relaxations. We show that the slow process appears in the GHz range only above the dynamic transition. The latter is seen to relate closely to the protein activity. We suggest that the protein is activated due to the slow process reaching GHz in frequency. Furthermore, the activation seems to happen at the dynamic transition of the solvent. This is an indication that the solvent plays the major role, and protein becomes its “slave”. So it is the structural relaxations, or equivalently the viscosity of the solvent that should dominate the bioactivity of a protein.; The fast process is ascribed to small conformational fluctuations. Unexpectedly, we observed that they could be suppressed more strongly in liquid glycerol than in solid trehalose at low temperatures. Observation of higher Myoglobin bioactivity in solid trehalose than in liquid glycerol at low temperatures suggests a relation between the fast relaxations and longer time bioactivities. Analysis on the pure solvents showed that there is a strong coupling of fast dynamics between the protein and the solvent. We suggest that the protein deactivation time (i.e. biopreservation) can be improved by optimizing the viscosity and the suppression of fast relaxations. By taking trehalose sugar, which has been optimally plasticized with glycerol as a model system, this idea has been proved valid. Molecular and theoretical pictures underlying the experimental observations have been discussed. |
