Protein contaminants of sodium dodecyl sulfate-polyacrylamide gels

Many artifacts and confusing results have arisen following the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and highly sensitive detection methods such as silver staining, in vitro iodination, and immunological reactions ("Western blotting"). Investigations into many areas of biology, from proteins tightly bound to DNA to common antigenic determinants of intermediate filaments, may have been affected by this confusion. Some who have suspected contamination believed 2-mercaptoethanol to be the source, but data in this report show that the contaminating proteins are skin proteins, especially keratins ranging from 54 to 57 kDa and 65 to 68 kDa.