[Molten globule unfolding by strong denaturing agents occurs by the "all or nothing" principle]

The equilibrium Gu-HCl-induced denaturation of bovine carbonic anhydrase B and beta-lactamase from Staphylococcus aureus was studied at 4 degrees C by the multiparametric approach. With the use of fast protein size-exclusion chromatography (FPLC) it has been shown that in the region of the molten globule-random coil transition the distribution function of the protein molecules on size is bimodal, i.e. the protein molecules (which are already denatured) can only in one of two conformational states. Consequently the unfolding of the molten globule can be of "all-or-none" character. This means that a protein molecule can be at least in three discrete states: the native, the molten globule and unfolded.