Precipitate proteins but not 1kDa peptide? - (Jul/24/2008 )
Is there a way to precipitate most of the larger proteins in a sample, but NOT precipitate a peptide of interest (approx 1kDa)? The peptide is adducted w/ lipids, so it would likely stick to size-selective spin columns, and I'm afraid that the yield would be too poor with size exclusion chromatography.
I think that most of the common protein precipitation methods won't work very well on such a low MW peptide. Try acetone, ethanol, methanol or chloroform. They have an advantage to be easily removed by evaporation so you won't contaminate your samples.
Have you tried ammonium sulphate?
I agree with swanny -- differential precipitation with ammonium sulfate is probably your best bet. There's a good overview in the Wikipedia article, including and online calculator for determining how to make solutions at a given percentage concentration of a saturated solution. Google "ammonium sulfate protein precipitation" for further info.