FAQ: I notice that the molecular weights I am observing are slightly different than those reported. Can you explain?

Apparent molecular weight values for the Blue Prestained Protein Standard, Broad Range can be different when run on different gel types and percentages. The reason for this disparity is due to the different formulations of various gels (buffering agents, ionic strength and pH). These differences are a result of the covalent attachment of dye to the proteins used in the standard. These molecules can carry a charge, changing the ability of the SDS to bind to the protein, as well as contributing to the protein’s overall charge. This altered charge will alter its mobility within the gel, which explains why prestained protein standards can run differently when run side by side with an unstained protein marker or ladder with similar molecular weights. We have analyzed NEB’s Blue Prestained  Protein Standard, Broad Range using a variety of commonly-used gel types. The results are shown below: