[RASMB] Songpon's diff+atp

[Lustig]

Dear Dear RASMB colleagues ,
Dear Songpon,
Question 1. I believe , if you  talk about  S  values you  mean  S° w,20 (I 
mean  S extrapolated to
Zero  concentration) .Alongated rod -stractur are very  concentration 
dependent, but  we have to be careful  with  extrapolation to zero conc., 
often at  low  conc. the  particle  may  dissociate in
subunits so this extrapolation  makes no sense.To proof this,  a row of  SE 
runs at  various conc. would  help to understand the system.
Diffusion runs are hard to trust in !  The best one  are those done 
with  schlieren optics at high conc. and  ideal in behavior . 
Non-symmetrical  and  conc. Dependent once includes  the diffusion 
coefficient  of more then the one conc. Diffusion  runs 
done  with  absorption optics have rarely
a good  baseline (to indicate precisely the net area  of such an  curve) 
what influences  mainly  the  value.
Diff. calculated  from s' and M` are not  accurate but  possible to use.
My opinion is  that 7.2 and 6.8  S° 20w !! are not too far from each other. 
If  M from SE can be
achieved  dont worry  about the  diffusion.

Questio 2.
My detergent experience is not  with LDAO, but only with Octyl Poe, 
DDM  and OG.
It is worth to read  the references and the problematic  use  of  detergents!!


A.Lustig, A.Engel,  G.Tsiotis ,E.M. Landau , W.Baschong. Molecular weight 
determination of membrane proteins by sedimentation equilibrium at the 
sucrose or Nycodenzadjusted density of the hydrated detergent micelle, 
Biochim. Biophys. Acta 1464 (2000)199-206

J.P. Rosenbusch , A. Lustig , M. Grabo, M. Zulauf  and M.Regenass, 
Approaches to determining membrane protein structures to high resolution: 
do selections of subpopulation occur?  Micron 32, (2001)75-90


Let say the detergent run is not the problem only  the ATP, so if possible 
why not to make such a run with  the  XLI or  model E with  interference , 
there the  ATP has no influence.
      I myself used  ATP solutions  with the XLA  but scanned at 285- 288 
nm.there the ATP
      has minor  influence. This is possible  if some  part  of your  prot 
absorbs at 280nm.
If not only the refraction  ....optics  can help.
What concerns the baseline, may be  the SEGAL computer program  may help
here is  the address
http://www.biozentrum.unibas.ch/personal/jseelig/AUC/index.html

with the intention to help.......yours.........ariel


Lustig Ariel
Biozentrum der Universität Basel
Klingelbergstr. 70
CH 4056 Basel
Switzerland
Dept. of Biophysical Chemistry  /
Analytical Ultracentrifuge Lab.TEL....+61 2672187
                                Fax    +61 2672189
E-mail   Ariel.Lustig at unibas.ch