Coomassie dyes, blue native

The dye Coomassie Brilliant Blue R250 nonspecifically binds to all the protein. The gel is soaked in the dye for it to seep in and bind to the proteins. The gel is then destained to remove the unbound dye. The dye binds to the protein and not the gel, and hence the protein bands can be visually seen. The binding of the dye to the protein is approximately in stoichiometry, so the relative amounts of protein can be determined by densitometry. For most SDS and native gels, separated proteins can be simultaneously fixed and stained in the same solution. 

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