Multiple enzyme forms from protein-bromphenol blue interaction during gel electrophoresis

Bromphenol blue (BPB)3 has been widely used as a tracking dye in disc gel electrophoresis since the early development of the technique (1). Although artifacts have been reported from protein-buffer interactions (2), and from residual ammonium persulfate (3,4), no such problems have been ascribed to BPB. We report here, however, that artifacts occurring during the electrophoresis of the enzyme, dihydrofolate reductase, apparently are due to the use of BPB. The ability of this dye to react with basic proteins at an alkaline pH (5) as well as some kinetic studies on the interactions of other dyes with albumin have been described (6). Thus, it is not unexpected that BPB might react with certain proteins during gel electrophoresis.