From: Peter Schuck <pschuck@helix.nih.gov>
  To  : rasmb@alpha.bbri.org
  Date: Sat, 04 Aug 2001 14:11:46 -0700

Re: wiggles in dc/dt plots

Gunther,
have you tried using direct boundary modeling, e.g. with the software
SEDFIT ? (can be downloaded from www.AnalyticalUltracentrifugation.com)
Peter

At 11:28 PM 8/3/01 +0200, you wrote:
>
>I would be interested if anyone could comment on the wiggles I observe
>regularily when I use DCDT to analyze velocity runs. They are tolerable if
>the protein concentration is high enough as in the example I have included
>in my mail. However it totally renders the option to run at low protein
>concentrations since a wiggle can not be separated from what might be a
>signal. Quite a shame since DCDT to my experience on other machines allows
>analysis down to protein concentrations of 10 micrograms/mL. Here a few
>comments on how the experiment was run. It is a monomeric protein with a MW
>of 45 Kda dialysed extensively against 100mM Tris, 1 mM TCEP and 50 mM NaCl
>pH8. I also know from dynamic light scattering that the sample has a few
>percent of nonspecific aggregates which give the signal at around 6S. The
>speed was 50Krpm at 25 dgrees. Data collection was set up to collect
>interference data as fast as possible. The graph shows the overlay created
>by using 20 adjacent scans. Unfortunatelly I can not release the name of the
>protein but it is not a specific property of the protein. I do observe the
>same when using BSA (first bitmap).
>Any comment how to avaiod this problem would be very well appreciated. 
>
>Thank you very much,
>
>Gunther Kern
>AZ R&D Boston
>Infection
>+781- 839 4611
>gunther.kern@astrazeneca.com
>
>
>