[RASMB] single species fit to heterodimer system

[D.Schubert]

Dear Joel,

why not use a two-component model: a 9.5 kDa component (which, in particular with a
1:1 mixture, probably would fit the mixture of the components quite well), and one of
19 kDa ? I think resolving A(r) into these two components would not be too
ill-conditioned and could give you all the answers you want to get.

Regards,
Dieter


Joel Mackay wrote:

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> hi all,
> I was just wondering if anyone happened to know off the top of their head
> what you might expect to see in the following situation.
>
> We have a mixture of two proteins that we think form a heterodimer. They
> are 11 kDa and 8 kDa. We have a 1:1 mixture of the two (in molar terms) and
> they have similar extinction coefficients (but not the same). We have run
> equilibrium experiments at several different speeds (22k, 27k, 35k),
> initially just to get a rough idea of the state of the interaction. I was
> expecting that if it was a very strong interaction, a fit to a simple
> single species model, using an averaged vbar, would yield a reasonable fit
> with a mass of ~19 kDa. If the interaction was weaker, i expected to see
> (using the same fit) a mass of somewhere between 10 kDa and 19 kDa, with
> perhaps a poorer fit.
>
> So, my question is: if the interaction was a moderate one (~10^5-10^6 M^-1,
> say) and it was well-behaved, what would you expect to happen to the
> molecular mass that you get from a single species model as you increase the
> speed? Would you expect it to increase? (This is what i think should
> happen, based on thinking and on having a play with Allan Minton's twocompsim).
>
> cheers
> joel
> *****************************************************************
> Dr Joel Mackay
> Senior Lecturer
> School of Molecular and Microbial Biosciences
> (formerly Department of Biochemistry)
> Building G08
> University of Sydney,
> Sydney, NSW 2006
> Australia
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--
Prof. Dr. Dieter Schubert
Institut fuer Biophysik der JWG-Universitaet
Theodor-Stern-Kai 7, Haus 74
D-60590 Frankfurt am Main
Germany
Tel. +49 (0)69 63017073
Fax  +49 (0)69 63015838