Protein Chemistry. Structure, Properties, and Research Methods - Shendryk A.N. 2022

Methods for Experimental Investigation of Protein Structure
Protein Separation Methods
Experimental Methods of Electrophoresis - SDS-PAGE

A highly useful variation of PAGE is the preliminary Treatment of a protein sample (or protein mixture) with sodium dodecyl sulfate (CH₃(CH₂)₁₀OSO₃^-Na⁺) (SDS) prior to gel loading. This technique is known as SDS-PAGE. SDS is an ionic surfactant with a negatively charged hydrophobic moiety (alkyl radical). Upon adsorption onto the protein surface, SDS induces Denaturation. The binding of SDS molecules to the peptide chain imparts a net negative charge to it. Furthermore, The amount of SDS bound to a protein is proportional to the size of its peptide chain. As a result, peptide chains of different sizes acquire nearly identical charge-to-size ratios (Q/r). When passing through the PAGE gel, which acts here as a molecular sieve, the denatured, SDS-coated protein molecules are "sieved" through the gel pores: smaller molecules move faster, while larger ones move more slowly. By comparing the electrophoretic mobility with that of SDS-treated reference Proteins of known molecular mass, SDS-PAGE allows the Determination of the molecular mass of an unknown protein, much like Gel filtration.