Hi Qing, If you have enough sample, you can just run a standard agarose gel with ethidium bromide. I've had a spectrum with peaks at 260 and 280 and the co-purifying RNA showed up clearly when I threw the fractions on an agarose gel.
Also check that your protein is expected to have a "normal" absorbance profile - if there aren't very many aromatics, especially Trp, then the peak protein absorbance may shift quite a bit (and also decrease), in which case the 260/280 rules shouldn't apply anymore. Hope this helps, Shane Caldwell McGill University On Wed, Jan 15, 2014 at 9:48 PM, Qing Shi <[email protected]> wrote: > Dear all, > > We all know that for purified protein, A260/A280=0.5, and for purified > DNA, A260/A280=1.8. Now my protein A260/A280=0.75, So I wonder if there is > DNA mixed with protein? Is there any way I can use to test if there is DNA? > > Thanks~ >
