ABSTRACT
In polyacrylamide gel electrophoresis (PAGE) proteins are applied to a porous polyacrylamide gel and separated in an electric field on the basis of their net negative charge and their size. Small/more negatively-charged proteins migrate further through the gel than larger/less negatively-charged proteins. In sodium dodecyl sulfate (SDS)-PAGE, the proteins are denatured and coated with an overall negative charge and thus the basis for their separation is only their mass. Isoelectric focusing electrophoretically separates proteins on the basis of their relative content of positively and negatively charged groups. Proteins can be visualized directly in gels by staining them with the dye Coomassie brilliant blue or with a silver stain. Radioactively-labeled proteins can be detected by overlaying the gel with X-ray film and observing the darkened areas on the developed autoradiograph that correspond to the radiolabeled proteins.
