SDS-PAGE is an analytical technique to separate proteins based on their molecular weight. SDS stands for Sodium Dodecyl Sulfate, a detergent. PAGE is the abbreviation of Poly Acrylamide Gel Electrophoresis. And this is where we get the combined term SDS-PAGE. Freshly SDS-PAGE gels are usually prepared before each experiment. Electrophoresis is a major technique for separating proteins and other substances such as nucleic acids, purines, pyrimidines, some organic compounds and even inorganic ions. Polyacrylamide gel is one of the main media. It is a porous gel whose pore size is close to the size of protein molecules, which improves the resolution of proteins. Moreover, the polyacrylamide gel has good chemical stability, strong repeatability, stability to changes in pH and temperature, and easy color observation.
Electrophoresis is a procedure that relies on an electric current to separate macromolecules, specifically in this case, proteins in a mixture. The separation here is solely based on the protein's molecular weights. Other influences on the rate of migration through the gel matrix include the structure and charge of the proteins. In SDS-PAGE, the use of sodium dodecyl sulfate and polyacrylamide gel largely eliminates the influence of the structure and charge, and proteins are separated solely based on polypeptide chain length. SDS polyacrylamide gel electrophoresis (SDS-PAGE) has the advantages of simple operation and good reproducibility in the determination of protein molecular weight, detection of specific proteins, and identification of strain species.
Proteins contain an overall positive or negative charge; this enables the movement of a protein molecule towards the isoelectric point at which the molecule has no net charge. By denaturing the proteins and giving them a uniform negative charge, it is possible to separate them based on the size as they migrate towards the positive electrode. When proteins are separated by electrophoresis through a gel matrix, smaller proteins migrate faster due to less resistance from the gel matrix.
After electrophoresis, protein separation cannot be directly observed by the naked eye, and subsequent staining techniques are needed. Coomassie brilliant blue staining and silver staining are common methods for routine detection and quantification of proteins separated by electrophoresis. After simple processing such as fixation-staining-decolorization, the distribution of protein can be clearly observed.
