I would like a good estimate of protein content in ultracentrifuge fractions of crude cell extracts. I know nucleic acids are present in some of them (I can see it on a ethidium bromide stained agarose gel in the fractions you would expect. There are rRNAs and possibly some genomic DNA as well. I'm sure along with other things not visible. For my purposes these contaminants are not a concern. I want to know about how much protein there is. I found something called the 'Warburg-Christian correction', what do protein people think? I am primarily an RNA guy.
agree with BCA method. it measures complexes of BCA with Cu+ ions generated after reaction with peptide bonds, so it is very specific for proteins with no interactions with nucleic acids
UV-visible absorbance is not a good idea in case of crude sample as several other factors absorb below 300nm. On the other hand any of the protein estimation method can solve ur problem.
Depends on how accurately you want to know protein concentration. The Lowry, BCA, and Bradford methods are highly idiosyncratic with regard to amino acid content of proteins, but are fine for crude estimations of protein concentration. Any reducing agents present will interfere with Lowry or BCA, detergents and lipids will interfere with Bradford. UV methods are superior for purified proteins (there are several), but these are probably not relevant for you if you have a highly heterogeneous mixture. The microbiuret method is the most accurate of the colorimetric methods in my opinion, but there are also some interferences from thiols, and it is not the most sensitive method.
Alternatively,try Pierce 660 nm Protein assay. In contrast to BCA, this is largely unaffected by most buffer components and detergents.(
http://www.piercenet.com/browse.cfm?fldID=C16B4598-5056-8A76-4E7D-ADABD3720DFE)
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