I am trying to quantify a 6 kda protein using western blot. I am getting a band at 50kda. I am using a 15% gel and probing with a monoclonal antibody. Please help.
Very small fragments are often difficult to see on SDS-PAGE.
First, you can go to more than 15% for your resolving gel (up to 20%), and avoid to make the bromophenol blue get out of the gel to be sure that your band won't also get out.
Second, you can use Tris-Tricine gels rather than Tris-Glycine ones, this usually lowers diffusion for very small fragments.
Check your antibody data sheet, it shows the band pattern. Some times you find the non specific bands also. Of-course it is non specific band. You shd run gel until dye front reaches the 2 cm before end. It is very small weight so some times we lost with the dye front. This protein usually run almost with dye front. I did the same and got the results