IONIC-STRENGTH-DEPENDENT TRANSITION OF HEN EGG-WHITE LYSOZYME AT LOW PH TO A COMPACT STATE AND ITS AGGREGATION ON THERMAL-DENATURATION

Equilibrium acid-induced unfolding of hen egg-white lysozyme has been investigated by a combination of optical methods, size-exclusion chrom atography, and differential scanning calorimetry. The results showed t he presence of a partially folded state of hen egg-white lysozyme at p H 1.5, characterized by a substantial secondary structure, a large sol vent exposure of non-polar clusters, and significantly disrupted terti ary structure. A large enthalpy was also associated with the conversio n of the acid-unfolded state to a fully unfolded state. Size-exclusion chromatography and 8-anilino-1-naphthalenesulphonic acid-binding stud ies showed an ionic-strength-induced transition of the partially folde d state to a compact conformation. Furthermore, an ionic-strength-depe ndent aggregation on thermal unfolding of the partially folded interme diate was also observed. These observations provide insights into the possible features responsible for the stabilization of intermediates i n the folding of hen egg-white lysozyme.