rule of thumb for SDS-PAGE separation of small proteins?

[Michael]

On Tue, 27 Oct 1998, scorbitt wrote:

> If you would like to increase your separation, I would reduce the percentage
> of acrylamide/bis in your gels.  Try a 10% or 12%.


> 

This would be right, if the proteins are about 90 kDa (800 amino acids) 
or more. For the small proteins this doesn't help at all. I would try a 
20% gel (no gradient). A gradient gel is usefull if you want to separate 
small and large proteins on the same gel. 


> >         I have to separate two proteins with 105 and 107 amino acids.  We
> > usually use a 16% Tricine SDS-PAGE.  But I sometimes don't get a
> > consistent separation.  I wonder if there is a rule of thumb for a small
> > protein separation?  Would a 20% gel be better?  Or maybe a 10% - 20%
> > gradient gel?  Ideally, the two bands should be at least 1 mm apart
> > after staining.
> >
> > Ing-Nang Wang
> >

Michael