absorbance value 1.05 at 260/280 while measuring the protein concentration at 280 nm, does it mean the protein solution contain dimers/oligomers or does it contain nucleic acid contamination?
No, not necessarily. The extinction coefficients at 280 and 260 nm depend on ratio between tryptophane, tyrosine, and phenylalanine.
For example, E.coli Initiation factor 3 does not contain any tryptophane but has several phenylalanines and its extinction coefficient at 260 is almost as twice as large as at 280 nm.
No, not necessarily. The extinction coefficients at 280 and 260 nm depend on ratio between tryptophane, tyrosine, and phenylalanine.
For example, E.coli Initiation factor 3 does not contain any tryptophane but has several phenylalanines and its extinction coefficient at 260 is almost as twice as large as at 280 nm.
If the protein have tryptophanes a ratio A260/A280 higher than environ 0.7 indicates nucleic acid contamination. Nucleic acids can interfere with your experiments, you can try to remove it as Oliver has suggested or additionally adding a washing step with high salt concentration.
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