Hello, I use from hand-cast polyacrylamide gel 14% and Bio-rad Precision Plus Dual Color Standard as MW Marker.My standard band and main band of my samples (somatropin) often are below 20 kDa and I dont know why?
Hello, Zahra. Are you using reducing or non-reducing SDS-PAGE? If you didn't treat your samples with ß-mercaptoethanol or DTT prior to electrophoresis, they may retain some tertiary structure and migrate a little faster than expected.
As with all forms of gel electrophoresis, molecules may be run in their native state, preserving the molecules' higher-order structure. This method is called native-PAGE. Alternatively, a chemical denaturant may be added to remove this structure and turn the molecule into an unstructured molecule whose mobility depends only on its length (because the protein-SDS complexes all have a similar mass-to-charge ratio). This procedure is called SDS-PAGE.
Also you can ry another standard https://www.thermofisher.com/order/catalog/product/26630
I compared protein standarts of different manufacturers and sometimes i obtained different data for commercially characterized proteine
Maybe, your antibody is not specific for your target protein, which was found to be the case for approx. 50% of commercially available antibodies (e.g. see: MONYA BAKER, Nature. 2015 May 21;521(7552):274-6. doi: 10.1038/521274a).
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