Conformation of interacting lysozyme by polarized and depolarized light scattering

The fluctuations of the polarized and depolarized light scattered by lysozyme solutions in acetate buffer and in 60% w/w glycerol-acetate mixtures have been studied by measuring the correlation function with a resolution of 12.5 ns. This result has been achieved by processing two replicas of the same scattered signal with two separate detectors and computing their cross correlation. The correlograms have been investigated at various temperatures and protein concentration at pH similar or equal to 4.6 and buffer ionic strength similar or equal to 45 mM. The rotational relaxation times obtained from depolarized scattering have been found to lie in the range 150-400 mu s, depending on the solution temperature, and no appreciable concentration dependence has been observed. On the other hand, the mutual translational diffusion coefficients derived from polarized scattering have been found to be strongly dependent on protein concentration. The main result is that the protein hydrodynamic radius, obtained by polarized photon correlation measurements is fully consistent with that estimated from depolarized photon correlation measurements, once the data are rescaled for temperature, viscosity, and the effects of protein-protein and salt-protein interactions. (C) 1999 American Institute of Physics. [S0021-9606(99)51204-X].