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another GST story #2

Matthias Zeiner mzei at sun0.urz.uni-heidelberg.de
Thu Jul 14 09:26:22 EST 1994

On 14 Jul 1994 13:29:03 GMT, Stephen R. Lasky wrote:

>I have been under the impression since my grad school days that proteins
>(after boiling in the presence of 2-mercaptoethanol and SDS) attain a
>relatively unfolded configuration and run as rods on SDS-PAGE.  I thought
>that this was the reason that sizes of proteins can be compared using the
>relative mobility on SDS-Page gels as opposed to native gels:  All the
>proteins have essentially the same shape as well as charge to mass ratio
>(due to the SDS).  I'd appreciate knowing if my impressions are incorrect.
>Stephen R. Lasky, Ph.D.       Brown University/Roger Williams Medical Center
>e-mail: Stephen_Lasky at brown.edu         LandLine: 401-456-6572
>America may be unique in being a country which has leapt from barbarism to decadence without touching civilization:  John O'Hara

It's not that easy. The charge of a protein is not necessarily proportional 
to it's molecular weight on a SDS gel. Modifications like phosphorylations 
or carboxy-methylations in fact do influence the run on a SDS gel. Also the 
gel system you use may play a role. I made the observation that the 
relative positions of the same two proteins to each other are different on 
30:1 and 60:1 PAA gels. Why? No idea!

Matthias Zeiner
Inst. Biol. Chem.

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