Polyacrylamide gel electrophoresis (PAGE) in the presence of the anionic detergent, sodium dodecyl sulfate (SDS), is probably the most commonly used technique for the analysis of protein mixtures. SDS is a very effective solubilizing agent for a wide range of polypeptides, including membrane proteins. It has been established that the majority of proteins bind 1.4 g SDS/1 g protein (1 ) to form negatively charged complexes. This results in masking of the intrinsic charge of the polypeptide chains, so that net charge per unit mass becomes approximately constant. Although the majority of proteins bind SDS in the expected ratio, it is important to realize that proteins containing nonprotein groups (e.g., glycoproteins, phosphoproteins, lipoproteins) can bind varying amounts of SDS, resulting in anomalous mobility and separation artifacts during SDS-PAGE.
