[RASMB] systematic differences

[Jack Kornblatt]

This note relates to systematic between cells in the AUC.

The problem, as I mentionned in my note, is that there is a difference in the determined s values of the same protein in different cells of AUC. This problem has apparently been seen by others as well. The question is: what is the cause of the problem? There is no firm answer. There is good speculation.

First, I would like to thank you all for your comments. I have followed your
advice. Cell 1 went into rotor position 2 and cell 2 went into rotor
position 1. The bias that was found when the cells were in their normal
positions (cell 1 in rotor position 1, etc) followed the cells; the data
are clean and clear.
In addition to the systematic difference between the s values that I find,
there is a systematic difference in the position of the menisci
(meniscuses). Cell 1 which uniformly gives an s value higher by 0.6% (from
stats) has a meniscus that is uniformly closer to the center of the rotor
by about .05 cm.
My gut feeling is that this should not in any way influence the values of
s that we determine so long as the meniscus is constant throughout the
run. Once I leave the gut, I'm hard pressed to find an explanation for why
the value of s should vary. I now apply a correction factor to the s values obtained in each cell.
 
Last point from a biologist. "I'm learning far more about analytical
ultracentrifugation than I ever thought I would want to."

All the best and thanks once more

jack
jack a kornblatt