ROLE OF SDS

Sodium lauryl sulfate, in science referred to as sodium dodecyl sulfate (SDS), is commonly used in preparing proteins for electrophoresis in the SDS-PAGE technique. Generally, the solution of proteins that is required to be analyzed is first mixed with sodium-dodecyl sulfate. When the proteins are treated with SDS, the polypeptide become rods of negative charge with equal charge densities or charge per unit length, and their separation is a function of the size differences only. When one never treat the proteins with SDS, different proteins with similar molecular weights would migrate differently due to differences in mass charge ratio, as each protein has an isoelectric point and molecular weight particular to its primary structure. This is basically known as Native PAGE. Thereby, adding SDS could solves this problem, as it binds to and unfolds the protein, giving a near uniform negative charge along the length of the polypeptide.

In additional, SDS bind in a ratio of approximately 1.4 g SDS per 1.0 g protein (although binding ratios can vary from 1.1-2.2 g SDS/g protein), giving an approximately uniform mass:charge ratio for most proteins, so that the distance of migration through the gel can be assumed to be directly related to the size of the protein only. Besides that, a tracking dye may be added to the protein solution so that the progress of the protein solution through the gel during the electrophoretic run can be monitored.