Visualization by chilling of protein bands in polyacrylamide gels containing 8 M urea: preparation and quantitation of foot-and-mouth disease virus capsid proteins

Protein bands become visible in polyacrylamide gels containing 8 m urea after chilling the gels in air for 5 to 10 min at ?70°C. Urea appears to crystallize preferentially as opaque bands in regions of the gel where protein reduces the amount of free water available as solvent for the urea molecules. Thus detected, the gel sections containing protein bands from foot-and-mouth disease virus can be immediately cut out, and their proteins obtained by electrophoretic elution or extraction procedures. Analysis of the proteins for purity and concentration is then carried out by electrophoresing measured aliquots on analytical gels, staining with Coomassie brilliant blue, scanning the gels for absorbance at 600 nm, and converting peak areas to micrograms of protein using Folin phenol standard curves determined for each purified capsid protein. The most basic capsid protein and its in virion proteolytic-cleavage products stain metachromatically.