[RASMB] aggregates data analysis

[walter stafford]

Hi Joris,

    Could you show us some scans on the approach to equilibrium?  What 
buffer were you using  (ionic strength, for example)? Is the protein 
highly charged under these conditions? You would expect to see this kind 
of linear behavior for a very non-ideal system. I would have to see the 
data before saying much more, however.

Walter Stafford
-------------

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Walter F. Stafford, Ph.D.
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Analytical Ultracentrifugation Research Laboratory
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Beld, Joris wrote:
> Dear all,
>
> I'm spinning a sample which shows -to me- surprising behavior. The raw data of a normal sedimentation equilibrium run of a protein looks always like a half-parabolic curve of the radius versus absorbance (x,y).
> However, this particular sample (protein) shows a different behavior in that the raw data look like a straight line taking off halfway the liquid column (absorbance almost zero) in the sector to the bottom of the cell (absorbance 0.7). Same behavior is reproducible at three different concentrations and three different rotational speeds (10,20,30 krpm).
> How should I interpret these data? Ultrascan does not really 'like' this data as input (although fitting is possible, the residuals look very bad, the fitted Mw -to a single species- is around 280kDa).
> Is this how a heterogeneous aggregating sample should look like?
> Thanks in advance.
>
> Best wishes,
>
> Joris Beld
> ETH Zürich
> Switzerland
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