[RASMB] density matching for PDC

[Mark Agacan]

I'm running AUC experiments with a membrane protein.
 
The detergent I am using has a relatively high value for vbar = 0.9747 (Maslennikov et al 2007)
 
I am trying to achieve a situation where the detergent contribution to the PDC buoyant mass is negligible (when the buffer density ~ matches the detergent density).
 
Buffer density = 1.00585
Detergent vbar = 0.9747 
 
Using the equation: 
 
p = 1/vbar-det
 
Detergent density = 1 / 0.9747 = 1.0258567
 
Is it valid to (a) increase the percentage of detergent in the buffer to increase the buffer density to match the detergent density (while remaining below the cMc)?, (b) add other non-interacting components into the buffer (d2o / h2o, sucrose, etc), and use e.g. SedNterp to calculate the correct proportions of these components to achieve the desired buffer density?
 
If the buffer and detergent densities are matched in this way, doesn't a velocity experiment provide accurate enough mass, without running equilibrium experiments?

And if the detergent does not absorb at 280 nm, won't absorbance measurements provide the protein-only mass of the protein-detergent complex? 
 
Many Thanks
 
Mark
 
 
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Dr Mark Agacan, Scientific Officer for the Division of Biological Chemistry and Drug Discovery,
Wellcome Trust Biocentre, College of Life Sciences, University of Dundee, Dundee, DD1 5EH 
Tel: +44 1382 386095    Fax: +44 1382 345764    Mobile: 07525 451 117
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