I need to know what is the most quick and easiest method/test to determine a protein purity after purification? I am tired from preparation and running the 1D SDS PAGE...
If you are suspecting of the impurities from DNA and RNA, just check the absorabance at 260/280nm.Also you can run the agarose gel for nucleic acid contamination.
If you are suspecting other proteins may contaminate your protein product, then the easiest way would be to just run the SDS-PAGE gel.
OR else
You could also do FPLC (Fast Protein Liquid Chromatography) and see what fractions come out. If there is more than one neat fraction, your protein might dimerise or multimerise in high concentration or there are other impurities present.
SDS-PAGE is the best general method. It can be done in an hour with mini-gels and colloidal Coomassie Blue stain (no destaining needed).
If you can standardize with a pure sample of the protein and if the protein has only one or two Trp residues, you may be able to use the tryptophan fluorescence intensity divided by the concentration as a test for purity.
I agree with Adam, Silver staining is a pretty sensitive and fast option (about 30'). Depending on the composition of your sample and the size of your protein you could also use directly MALDI mass spectrometry (MS), with or without prior digestion. SELDI is a version of MALDI with special chemical capture plates but I doubt you would need that. MALDI MS is really fast and would allow you to see the most abundant protein in your sample. However, if protein contaminants are present in low amounts (compared to your protein of interest) you may not be able to see them due to the dynamic range of these techniques (both 1D/commasie/silver and MALDI). If you are really interested in assessing the presence of small contaminants there could be more thorough ways to control for that (such as LC-MS on a ion-trap and perhaps equalizer beads).
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