[RASMB] everything sediments... some things float

[Borries Demeler]

> 
> Hello everybody,
> 
> recently, a sample finally found its way to me that has floating AND 
> sedimenting (macromolecular) components. Both are detected and it is 
> important to characterize both, at least their partial concentrations. 
> So.... did I mention already that both fractions are polydisperse?
> 
> As far as I'm aware, no Lamm-equation based algorithm will calculate a 
> distribution going from negative to positive. Please do correct me if 
> I'm wrong!
> I've performed synthetic boundary runs, so at least I have data with 
> upper and lower plateaus. Any suggestions on how to treat these data in 
> a model-independent way, i.e. where to put the (permeable) meniscus? 
> (Walter, my hopes are somewhat resting on Sedanal...?)
> Have the ancient masters encountered anything like that before? How did 
> they deal with it?
> 
> Best wishes to all of you,
> Holger

Holger,

2-dimensional spectrum analysis can handle heterogeneity simultaneously in
both sedimenting and floating samples in a model-independent way insofar
as there is no surefire way to model-independently determine molecular
weight, since in such cases you will likely also have a heterogeneity in
vbar. Since vbar and MW are 100% correlated, you will need to fix one
or the other. But other than that constraint, 2DSA will allow you to
analyze the data in a model-independent way for partial concentration,
s, D and f/f0 for each species. You also have to deal with cases of s
where |s| is smaller than 0.1, which cannot be reliably separated from
a mere baseline absorbance. Adding time-invariant noise fitting will 
handle the baseline contributions.

You should contact Emre Brookes (emre at biochem.uthscsa.edu) for help on
how to best represent that condition in the USLIMS interface.

-Borries