Help! Cell homogenization and protein extraction for Western Blotting - (Feb/07/2011 )

I'm working with primary mouse hepatocytes.
Currently I'm having a trouble with protein extraction from my cell culture.

I usually add Tris-HCl lysis buffer (supplemented with sucrose, KCl, MgCl2) and sonicate the samples.
However, when I spin the samples in the centrifuge, no matter how fast I spin them down, I get white stuffs (guessing genomic DNA) coagulated on top of the cell lysate.
This gives me a so much trouble for Bradford assay and loading samples on gels for Western Blotting.

Is there any ways to get rid of them?

Thank you

movement K on Mon Feb 7 16:08:10 2011 said:

i would think that the floating white material is lipid or carbohydrate.