MOLTEN GLOBULE MONOMERS IN HUMAN SUPEROXIDE-DISMUTASE

The time-resolved fluorescence decay and anisotropy of Cu/Zn human sup eroxide dismutase (HSOD) were studied as a function of temperature and denaturant concentration. In addition, circular dichroism (CD) measur ements were performed on HSOD as a function of denaturant concentratio n in the amide and aromatic regions. The time-resolved fluorescence de cay results reveal the existence of structural microheterogeneity in H SOD. Furthermore, CD measurements and a global analysis decomposition of the time-resolved fluorescence decay over denaturant concentration shows the presence of an intermediate in the unfolding of HSOD by guan idinium hydrochloride. Considering our previous measurements of partia lly denatured HSOD as a function of protein concentration (Mei et al., Biochemistry 31 (1992) 7224-7230). our results strongly suggest that the unfolding intermediate is a monomer that displays a molten globule state.