Differential light scattering technique for the study of conformational changes in macromolecules

We present the design and development of a differential laser spectrometer capable of the accurate measurement of very small changes in the translational diffusion coefficients (DT) of macromolecules. Since DT depends solely on the translational frictional coefficient of a macromolecule, this parameter is a direct measure of macromolecular conformation, and thus detection of small changes in the translational diffusion coefficient can reveal very slight conformational alterations. The differential laser probe we present is a differential optical mixing laser spectrometer capable of the direct measurement of the difference in the spectra of the light scattered by two solutions of macromolecules and hence, the difference in the translational diffusion coefficients of the macromolecular species under investigation. In its present form, the instrument has a precision of 3 parts in 103, that is, the differential laser probe can measure a change in DT of 3% with a precision of 10%. Discussion is provided for the system improvements required to increase the precision one additional order of magnitude.