2-Merceptoethanol is suitable for reducing protein disulfide bonds prior to polyacrylamide gel electrophoresis and is usually included in a sample buffer for SDS-PAGE. 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.