From: Jo Butler <pjgb@mrc-lmb.cam.ac.uk>
  To  : hjl , rasmb@alpha.bbri.org
  Date: Thu, 22 Mar 2001 10:21:40 -0000

Re: a question

Dear HJ,

For a dimerisation reaction, the ASSOCIATION constant (Ka) is given by the 
equation:
Ka = c2 / c1**2 ; where c1 and c2 are the monomer and dimer concentrations 
respectively.  (The DISSOCIATION constant, Kd, is the inverse of Ka.)
When you are using this equation to calculate concentrations, you need to 
be careful about units.  In the strict form, both c1 and c2 are in units of 
molarity (or molality).  This means that you need to remember that the 
dimer has 2x the molecular mass of monomer (and, to a reasonable 
approximation, also 2x the molar extinction coefficient), if you want 
weight fractions.

Jo

--On Thursday, March 22, 2001 11:44 am +0800 hjl <hjlee@ndmctsgh.edu.tw> 
wrote:

>
> 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.
> HJ
>
>



P.J.G. Butler,
MRC Laboratory of Molecular Biology,
Hills Road, Cambridge, CB2 2QH, UK.
Tel. +44 (0)1223 402296