no band in 6% gel - (Oct/01/2007 )

hi I have avery big problem which is :
I inject yhe same sample in 12% gel and 6% gel there is band appear in 12% gel in high molecular weight but no band in 6%
and also the band in 12% is faint
also the front line doesn`t appear after destain
I don`t know what is the problem
is it in the cell of electrophoresis or power supply or in the stain or in the gel itself or in the running bufffer or in the loading buffer
please any one reply me my time is waste I repeat this run 4 times and every time give bad result
thanks

I think you should change the power supply, running buffer and loading dye.
Then you might solve your problem.
All the best

Also if they are home made gels you should check the pH of upper and lower TRIS.
All the best.

surrisingly no molecular weight marker shows up in 6% gel...
i did lots of 6% gels (in tris glycine running buffer) and at least i was able to show the bromophenol blue line...
did you check the migration ? a possibility of over migrating?
you may also load more proteins (till 30µg if feasible)

thank yoy very much for all
I observe the migration , no over migrating occur
about the power supply, I ask the supervisor and he tell me no problem
I ask: is the sepration of protein affected by content of gel (APS,or other component) even the gel is polymerized well
the running buffer is the same I used before
about loading more proteins it is useless because I compare between the same samples by the same concentration but in different period(after 1 month,2month,and so on)
so when I load more protein the band well differ in concentration and no compare success
what is your opinion?
also I want to ask is the protein of meat preserved in - 20 c is affected by the time ,is the protein affected or change after 6 month
please if anyone reply on question number 2 send me refernce of that
thank you very much