Artefacts associated with Nonidet P‐40 upon sodium dodecyl sulphate polyacrylamide gel electrophoresis of protein

One‐dimensional sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) of protein in the presence of Nonidet P–40 (NP–40) induces vertical streaking which breaks horizontal bands of protein to produce a “multiple spot” effect. The same effect can be induced upon high resolution two‐dimensional electrophoresis if the NP–40 concentration of the first‐dimension isoelectric focusing (IEF) gels is increased to 4 % w/v and the gels electrophoresed (SDS‐PAGE) without SDS‐equilibration. The relevance of this phenomenon as regards interpretation of two‐dimensional electrophoretic patterns is discussed.