Hepatitis B surface antigen polypeptides: artifactual bands in sodium dodecyl sulfate-polyacrylamide gel electrophoresis caused by aggregation.

Hepatitis B surface antigen, subtype ad, was purified and studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Two major bands with molecular weights of 23,500 and 27,500 and several weaker bands with higher molecular weights were observed. When the low-molecular-weight bands and the group of high-molecular-weight bands were excised from the gel, eluted, and reelectrophoresed, neither the low-molecular-weight bands nor the high-molecular-weight bands ever appeared alone, but both high- and low-molecular-weight bands always appeared. It was concluded that the apparently high-molecular-weight bands represented aggregates of the two small polypeptides whose monomers formed the major bands. The preparation thus contained only two polypeptides.