[RASMB] difference between experimental and modelled sed coef for protein-DNA complexes

[Peter Schuck]

Marcelo,

Dependent on the rotor speed you've used, I also think it is possible that 
the glycerol will sediment and form density and viscosity gradient.   I 
would do an experiment like Borries suggested and run the glycerol/D2O 
mixture against water in the XLI.  If you see a gradient forming, it likely 
will significantly influence your macromolecular sedimentation.   I've 
recently examined such effects in theory.  You can find a description of 
the results and a SEDFIT model how to quantitatively take this into account 
when modeling at
http://www.analyticalultracentrifugation.com/inhomogeneous_solvent.htm

Another problem could be that at the high concentration of glycerol you 
might run into effects of preferential hydration leading to deviations of 
your v-bar from the calculated one.

Best,
Peter