incomplete separation - (Mar/13/2008 )

Hi: I really need help. I run a 12.5% SDS-PAGE but in the stained MW just appeared a band corresponding to 42KD, the others 3 bands doesn`t appear. It`s like the the protein separation stop at 45 KD. When I transfer to nitrocellusose membrane , I stained with punceau and just appear the proteins corresponding to this MW. thank you!

are you running until the tracking dye reaches the bottom or exits the gel?

are your buffers okay?