2-Mercaptoethanol is used to reduce disulfide linkages in solubilizing proteins for gel electrophoresis (typically used in SDS-PAGE sample buffer at 5% concentration). Also it reduces excess oxidative polymerization of catalysts. Cleaving intermolecular (between subunits) disulfide bonds allows the subunits of a protein to separate independently on SDS-PAGE. Cleaving intramolecular (within subunit) disulfide bonds allows the subunits to become completely denatured so that each peptide migrates according to its chain length with no influence due to secondary structure.In solution, 2-mercaptoethanol is readily oxidized in air to a disulfide, especially at alkaline pH. Because of this property, it is widely used to protect proteins, enzymes in particular, from becoming inactive. An excess of 2-mercaptoethanol (generally used at 0.01 M) will maintain the protein thiol groups in their reduced state.