[RASMB] Loading concentration

[Borries Demeler]

> 
> Hi, 
> 
> I got my data for equilibrium analytical ultracentrifugation. It
> turned out the absorbance of my protein is below 0.1 (OD280). Are
> these data still analyzable? And what is the optimum range for
> equilibrium analytical ultracentrifugation? Thanks a lot.
> 
> 
> Lin

Lin,

you can probably shift the wavelength to 230 nm or lower to see if
your protein absorbs better. You need to make sure that your buffer
doesn't absorb at the lower wavelength. I generally include absorbance
data up to 0.9 OD, give or take a few dependening on wavelength intensity.

less than 0.1 OD sounds almost like nothing. At this OD 10% of the signal
is noise which is too much to get reliable analysis for any system.

It is best to use multiple concentration measurements and include all
of them in your global fit. I generally use 2 6-channel cells with 
0.3, 0.5 and 0.7 OD 230 and 280. This gives me a broad concentration
range over which I am analyzing the sample. For many cases this works
very well. If you don't have aromatic sidechains in your protein, your
mileage may vary at 280 nm.

Good luck, -Borries