[RASMB] Negative Slope on Sed Eq data

[Jo Butler]

Dear Erin,

You do not describe either your protein or the solvent.
Depending upon these, your results could be perfectly valid - if the 
protein has a lower density than the solvent, it will float rather than 
sedimenting.  This is not just fanciful - many lipoproteins have lower 
densities than water.
One important thing to note is that the standard sedimentation equations 
still apply - it is just that (1 - v-bar*rho) is now negative.

Jo

--On Friday, December 6, 2002 12:04 pm -0500 Erin Matthews 
<erin.matthews at yale.edu> wrote:

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> I'm currently running a sed. equilbrium experiemnt on an 8kD protein,
> and to my surprise, the slope of the data curves downwards (the
> absorbance at the meniscus is about .4 AU and the absorbance at the
> bottom of the cell is .2 AU).  What am I doing wrong?
>
> Erin Matthews
> Grad Student, Engelman Lab
> Yale Univeristy
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P.J.G. Butler,
MRC Laboratory of Molecular Biology,
Hills Road, Cambridge, CB2 2QH, UK.
Tel. +44 (0)1223 402296