Guanidine hydrochloride induced reversible dissociation and denaturation of duck delta 2-crystallin

The tetrameric delta 2-crystallin from duck lens exhibits a reversible diss ociation-denaturation process in solutions containing guanidine hydrochlori de (GdnHCl). Sigmoidal or biphasic curves for the dissociation/denaturation processes, obtained using different methods of structural analysis, as a f unction of GdnHCl concentration were not coincidental with each other. delt a 2-crystallin in 0.91 m GdnHCl existed primarily as a monomer, which had n o endogenous argininosuccinate lyase activity. After dilution of the GdnHCl -treated protein, the monomers reassociated into tetramers with concomitant recovery of enzyme activity. The sigmoidal recovery of enzyme activity dem onstrates a cooperative hysteretic reactivation process. When the concentra tion of GdnHCl was higher than 1.2 m, various partially unfolded soluble fo rms of delta 2-crystallin were produced from the dissociated monomers as sh own by size-exclusion chromatography. The formation of a partially unfolded intermediate during the dissociation-denaturation process is proposed.