Non-native conformations of proteins were generated by temporary contact with aqueous solutions of sodium dodecyl sulfate (SDS) and separated from the native state with capillary zone electrophoresis (CZE) in alkaline borate buffer deficient of SDS. Nine proteins at concentrations of 2.0 or 3.0 mg (center dot) L-1 were compared in terms of their susceptibility to SIDS. For superoxide dismutase and ferritin the tendency of unfolding was modest with < 25% of the protein being transformed to the non-native state at 10 mmol center dot L-1 SDS. Highest susceptibility was observed for albumin, myoglobin (Mb), and hemoglobin with > 75% in the non-native state even at 2.0 mmol center dot L-1 SDS. The influence of varying SDS concentrations on the conformational state of Mb was tested. Increasing the SDS concentration, circular dichroism revealed a reduction in a-helix, an increase in random coil, and an introduction of P-sheet, which is absent in native structure. Modifications in the secondary structure were in agreement with distinct changes in the shape of the non-native Mb peak in CZE and make a gradual unfolding/refolding process with several coexisting molten globules instead of twostate transition of conformations most plausible for Mb. CZE was found to contribute to a further understanding of holo-Mb transformation towards a population of nonnative conformations (i) by means of calculated peak area ratios of native to non-native states, which showed sigmoid transition, (ii) by detecting the release of the prosthetic heme group, and (iii) by changes in the effective electrophoretic mobility of the MbSDS peaks. Reconstituted holo-Mb forms differed in the Soret band around 410 nm, indicating diversity in the conformation of the heme pocket.