4 x Protein Loading Buffer is added to solubilized protein samples prior to analysis by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). SDS detergent denatures the proteins and gives each an overall negative charge enabling proteins to migrate accordingly to their length. 2-Mercaptoethanol reduces the disulphide bonds. Glycerol increases the density of the sample so that it layers in the sample well. Bromophenol blue runs ahead of the proteins.