From: Borries Demeler <demeler@bioc09.v19.uthscsa.edu>
  To  : hjlee@ndmctsgh.edu.tw
  Date: Thu, 22 Mar 2001 05:24:40 -0600 (CST)

Re: a question

> 
> Hi,
> 
> I am a freshman using sedimentation equilibrium to spot the dissociation =
> problem of my protein. From the data fitting to self-association, I met =
> the problem about how to correlate the available association constant to =
> the percentage distribution of oligomer and monomer in the solution. I =
> will be appreciated if anyone can tell me how to calculate that.

The UltraScan software (http://www.ultrascan.uthscsa.edu) will calculate this
distribution for you for the general case of a monomer/N-mer/M-mer association.
You can find some screenshots and a manual page at:

http://www.ultrascan.uthscsa.edu/manual/sassoc.html (manual page)
http://www.ultrascan.uthscsa.edu/manual/sassoc-1.gif
http://www.ultrascan.uthscsa.edu/manual/sassoc-2.gif (calculation mode)

Keep in mind that the answer is dependent on concentration For the case
of the monomer-dimer problem, the calculation is trivial, it's just the
solution of a quadratic:

C_total = C_monomer + C_dimer (1)

K = C_dimer/C_monomer^2       (2)

substitute and rearrange:

K*C_monomer^2 + C_monomer - C_total = 0 (3)

This is in the form of a quadratic (ax^2 + bx + c = 0) and can be solved
with [-b +/- sqrt(b^2 - 4ac)]/2a for C_monomer. Then substitute C_monomer
in (1) and you have C_dimer.

hope that helps, -Borries
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* Borries Demeler                                                             *
* The University of Texas Health Science Center at San Antonio                *
* Dept. of Biochemistry, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900 *
* Voice: 210-567-6592, Fax: 210-567-4575, Email: demeler@biochem.uthscsa.edu  *
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