Dynamic light scattering apparatus

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We all receive the same email message.  It says, "size matters".  What the message does not tell you is that shape also matters.  Two complementary techniques, analytical ultracentrifugation and dynamic light scattering (DLS) allow one to quantify the size and shape of biological macromolecules and view, for a constant molecular weight, how size and shape change as molecules go about doing the things they do.  We have an analytical ultracentrifuge and are reasonably experienced at using it.  We do not have a DLS apparatus. Dynamic light scattering for biochemists is important in three different situations: (1) It allows one to determine how big the individual molecules in a uniform collection of molecules appear to be. It yields a diffusion coefficient, which can be related to the size of an equivalent sphere.  (2) If the molecules in the collection are not uniform but consist of multiple species, the largest of the species contributes the strongest signal in the data analysis; this information is essential when evaluating samples for crystallization.  (3) If a solution contains rapidly interconverting multimers of monomers, the data yield an average value of the size of the particles that is a function of the equilibrium position between the monomers and multimers.   If we now combine this data with that from the analytical ultracentrifuge and the molecular weight (from mass spectroscopy or sequence analysis), the global analysis from these independently determined experimental parameters  permits us to pinpoint how the molecules change shape, size and hydration as we subject them to changing environmental conditions.  Situation (1) is central to all the applicants, situation (2) is relevant to Peter Pawelek's work and situation (3) is relevant MJ Kornblatt, Pawelek and Turnbull.