Theoretically, if the value of A260/A280 goes high it shows DNA contamination in protein sample, and if goes down (0.6-0.8) it shows good purity of protein. In this way, a value less than 0.6 should show a more pure protein. but lower value of A260/A280 of protein
It probably indicates that the protein solution is contaminated with some small molecule that absorbs more strongly at 280 nm than at 260 nm. If so, the contaminant can probably be removed by dialysis or gel filtration.
Yes, it indicates protein contaminants. Nucleic acids have a higher absorbance at 260 nm than proteins, so a low A260/A280 ratio suggests that the sample contains more nucleic acids than proteins.
Yes, a A260/A280 ratio below 0.5 is an indication of contamination. It typically signifies that the sample contains large amounts of carbohydrates and/or phenolic compounds.
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