Blurred low molecular weight bands in SDS-PAGE - Need your help (Aug/24/2009 )

Hello Friends,

I cast and run 12% SDS-PAGE gels for plant protein extracts. Low molecular weight proteins bands of my gels are always blurred while the high MW bands appear fine. This effect is common for pre-stained MW markers too.
I'm wondering whether my gels are bad. I always allow gels to polymerize overnight at room temperature. Could this be a problem with insufficient amount of TEMED and/or ammonium persulfate?
I greatly appreciate your suggestions and comments.

Thanks.

no. it is just the nature of electrophoresis (it may also be caused by insufficient stacking, buffers being "off",...)

there are a couple of ways to combat this.

one is to use a gradient gel (5-15%, 10-20%, 10-15%,...).

another is to add urea to the formula.

i prefer gradients.