Four major isoforms of the BR96 antibody were separated by micellar electrokinetic capillary chromatography. Heat-induced reversible isoform interconversions were observed at 70 degrees C, and after extended incubation at 80 degrees C, all species irreversibly transformed into a new single peak. In the presence of sodium dodecyl sulfate (1.0 mg/mL), the isoform transformations occurred at lower temperatures without altering the separation pattern. Size exclusion chromatography analysis detected no aggregation at temperatures below 80 degrees C. Parallel circular dichroism measurements indicated significant conformational changes at 70-80 degrees C. The parallelism between isoform transformations and secondary structure changes allows consideration of CE-separated isoforms of BR96 antibody as conformers, an equilibrium between which can be shifted by different physicochemical factors such as elevated temperatures and amphiphilic surfactants.