Protein quantification with Ammoniumsulfate present?!

[Bill Bowers]

Hi Christoph,

There is a commercial copper/biuret based protein assay which claims no 
interference up to 40% ammonium sulfate.  It uses a "universal 
precipitant" to pellet protein first.  No claim is stated for precision, 
but the standard curves published look good with a threshold sensitivity 
of 0.5ug protein/tube.  It is called the "Non-Interfering Protein 
AssayTM", sold by Geno Technology, Inc. 3830 Washington Blvd, St. Louis, 
MO 63108, USA tel 314-534-0075 fax 314-534-1147.

Another option is to diafilter your fractions in centrifugal 
concentrators.  We offer a simple, cost effective reusable microfuge 
system which accepts up to 750uL and concentrates rapidly to 7uL with 
quantitative recovery.  If you are interested, the system is described at 
http://www.orbio.com.  You can Email me for information about distribution 
in Germany.

Best regards,

Bill Bowers

In article <35726aaf.702161 at news.fu-berlin.de>, 
deleteme_cpeter at zedat.fu-berlin.de says...
>
>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)