Casein Zymography- green/yellow line following dye front - (Sep/22/2006 )

I'm running Casein Zymography gels (12% Acrlyamide) on bovine extracts. When the dye front has run off the gel there is still a yellow/green line about 1/3- 1/2 way up the gel. We have ruled out temperature flucuations and gel composition as possible problems. It is most likely a pH problem and that is what I will be looking into next but I was wondering if anyone had experienced anything similiar and if so how was it rectified?

there should be some more information...what kind of gel-system/buffer-sytem is running? what is the dye? bromophenol blue?

The sample buffer that I am using is 150mM Tris (pH 6.8), 20% Glycerol, 0.02% bromophenol blue and 0.75% mercaptoethanol. The running buffer is 25mM Tris-HCl, 0.05% mercaptoethanol, 192mM glycine, 1mM EDTA and is pH to 8.3. I'm applying 100V for ~4 hours and running the entire system at 4 degrees C. The gels themselves are composed of 37:1 acrylamide:bisacrylamide, tris and water. The resolving gel contains 0.21% casein. I have not added SDS to any part of the system at this stage as SDS affects the activity of the calpains but I am going to try to add SDS to the sample buffer and running buffer this week and incubate the gel with Triton X prior to placing it in 10mM CaCl2 development buffer.