3-STAGE EQUILIBRIUM UNFOLDING OF SMALL GLOBULAR-PROTEINS BY STRONG DENATURANTS .2. BETA-LACTAMASE AND GENERAL-MODEL

Equilibrium unfolding of staphylococcal beta-lactamase induced with gu anidinium hydrochloride at 4 degrees C was studied by circular dichroi sm, enzymic assays, fluorescence, and high-performance gel permeation. Like in the case of carbonic anhydrase B, it proved to be a three-sta ge process involving at least two intermediate states: molten globule and its folding precursor (''pre-molten globule'' or partly folded sta te) with structural properties intermediate between those of molten gl obule and random coil. The new intermediate is supposed to be an equil ibrium analog of the first kinetic intermediate observed in protein fo lding.