Help with SDS page

[sapo]

I´m work with membrane protein. Realize a sds page, after protein quantification by Bradford. This quantification gave concentrations in the range of 4 microg / microL of protein in my sample, but to make the gel (loading 50 ug of protein) does not see any band just a blast. Maybe the bradford quantify proteins degraded partial or total?

[5µl-pipette_death_punch]

Have you checked the pH-value of loading buffer (6,8) and pH Value of Tris buffer in the Stacking Gel (6,8) and the Tris buffer in the resolving gel (8,8). I hope this hint is not insulting to you and I guess you have done in the correct way. But what you tell us sounds exactly like there was now pH difference between the 2 gels.