Protein quantification with Ammoniumsulfate present?!

[Christoph Peter]

Hi!

I am doing hydrophobic interaction chromatography with ammoniumsulfate
and need to quantify the protein content of the fractions (down to 20
microgram/ml) which contain 0-3M ammoniumsulfate. Bradford gives
unreliable results, no matter what I use as a blank. BCA and BioRads
DC-Assay do not work at all with AS present. Protein precipitation
with TCA prior to Bradford gives some sort of linear standard curve
but only with a high standard deviation and not very reproducible. I
am currently trying UV 260nm and SDS-PAGE scanning, but both have
severe drawbacks (sensitivity and time/labour intensity, resp.).

Does anybody have any proposals about how to get a reliable protein
concentration in samples containing ammoniumsulfate from 0 to 3 M?

Thanks in advance.....
--
Christoph Peter
PhD Student (Biotechnology)
cpeter at zedat dot fu-berlin dot de

>Alles wird gut!<(Beate)