Effect of guanidine hydrochloride on the conformation of egg yolk low density lipoprotein

The denaturation of egg yolk low-density lipoprotein (LDL) induced by guanidine hydrochloride (GdnHCl) has been investigated by using circular dichroism (CD) and fluorescence measurements. The transition curves were obtained from changes of the residue ellipticity at 222 nm and the fluorescence intensity of the aromatic residues, tyrosine and fluorescence. Different transition curves were obtained at the molarities of GdnHCl between 2 and 6 M, and between 1 and 4 M from the CD and the fluorescence measurements, respectively. The noncoincidence of the transition curves as well as the asymmetry of the transition curve obtained from the fluorescence measurements suggests that the denaturation process of LDL consists of several transition states. A very low apparent free energy of denaturation (delta G(app) H2O = 3.0 kcal mol-1) obtained by CD data suggests that LDL has an unstable folded structure in its native state.