From: Hiroshi Fujita <lvl79@mbox.kyoto-inet.or.jp>
  To  : rasmb@bbri.harvard.edu
  Date: Sat, 01 May 1999 11:28:36 +0900

On the determination of D

Dear RASMBers:
I am quite interested in seeing the discussions going among our members on the determination 
of D from sedimentation velocity experiments. Although I know little about recent progress in 
ultracentrifugal analysis, it seems that the UC people of my generation well recognized 
how risky it is to try this determintion for macromolecular solutions,　because boundary 
spreading is so sensitive to heterogeneity and the concentration dependence of s. Thus, since 
the early 1970s, the dynamic light scattering (DLS) has replaced the ultracentrifuge and also  
the classic diffusiometer as the convenient and standard method for D of polymer as well as 
protein solutions.  I strongly suggest protein physical chemistry to get familar with DLS 
in both theory and experiment.
Even with the D data from DLS the application of the Svedberg relation (for the calculation of 
M ) to systems whose homogeneity is doubtful is risky because this relation is valid only for 
strictly binary solutions (its form for multi-component systems is quite complex and does not 
allow easy application).  Such D data give information equivalent to the s data from　the 
ultrcentrifuge more rapidly and hence more conveniently. I wish the UC users of the younger 
generation to learn the historical developments of sedimentation analysis since the Uppsala 
days. 
Sincerely yours,
Hiroshi Fujita 

Hiroshi Fujita
35 Shimotakedono-Cho, Shichiku, Kita-Ku
Kyoto,　Japan
Phone/Fax：075-491-2061
e-mail:lvl79@mbox.kyoto-inet.or.jp