Specific features of the temperature behavior of lysozyme diffusivity in solutions with different protein concentrations

The paper presents dynamic light scattering investigations of the temperature behavior of lysozyme diffusivity in solutions with different protein concentrations. The objects are lysozyme solutions with concentrations ranging from 10 mg/ml up to 250 mg/ml; each sample has been studied at temperatures increasing from 15° to 55 °C. The analysis of the autocorrelation functions obtained by DLS for all the solutions has revealed two types of motion with different relaxation times: a fast mode that corresponds to the diffusion of lysozyme molecules and a slow mode associated with the motion of clusters, i.e., complexes consisting of several protein molecules. It is shown that the temperature dependences of the diffusion coefficient of lysozyme in all the solutions are well described by the Arrhenius law. The temperature behavior of the relaxation time of the slow mode has been found to be different for the low- and high-concentration lysozyme solutions. The low-concentration protein solution is characterized by a monotonous decrease in the slow mode relaxation time with increasing temperature. As the lysozyme concentration is increased to 100 mg/ml, a considerable change is observed: a minimum in the temperature dependence of the relaxation time of the slow mode appears. Possible reasons for such a behavior of the lysozyme diffusivity are discussed.