[RASMB] Chaos Summary & Quest.

[H. Olin Spivey]

Dear Friends,

    I have a summary and a related questions concerning the chaotic 
behavior I described in the message of 11/16/01.

    I received only two suggestions as I recall.  They suggested that 
it was probably convection considering its pattern and behavior.  I 
agree.  I don't see how it can be anything else, but find it strange 
that it should occur only with this sample and not the thyroglobulin 
control with a similar molec. wt.   Perhaps it is due to the slow 
association equilibria in this protein we are studying.  If the 
centrifugal distribution is faster than the chemical equilibration, 
could this lead to an unstable density gradient that keeps recurring 
in time?  This is more than I can rationalize now.  If my colleague 
whose protein exhibits this chaotic behavior desires, we will run the 
next sample with a density stabilizer.

    What do you recommend for this density stabilization for 
absorption optics?  We don't want to use high concentrations of 
stabilizers, e.g., sucrose, which will alter the activity coefficient 
of water and thus possibly affect the extent of self-association of 
the protein.  Metrizamide has far too much absorbance at 280 nm to 
use.  Allen Minton has used 0.25-0.75% polyethyleneglycol 20,000 and 
4,000, 0.25-0.5% T-70 dextran, and 0.5% sucrose with his preparative 
centrifuge method.  However, it isn't clear from the results if any 
density stabilization was necessary.  I don't know which of these 
provides better density stabilization in principle - does one of you? 
I suspect that the higher MW substances provide the density 
stabilization quicker in time, which might be important in this case. 
Of course we will test a series of concentrations of this stabilizer.

    One of my most pleasant blessings is the marvelous communication 
and help this RASMB provides.  This makes research fun.  Thank you 
all and best wishes to you for a merry season and new year,

Olin

-- 
H. Olin Spivey                       Phone: (405) 744-6192
Dept. Biochem. & Molec. Biology      Fax:   (405) 744-7799
246 NRC                              Email: OSpivey at Biochem.Okstate.Edu
Oklahoma State University
Stillwater, OK 74078-3035