NACL-INDUCED CONFORMATIONAL TRANSITION OF THE ACID-UNFOLDED STATE OF STAPHYLOCOCCAL NUCLEASE

The add-unfolded state (U-A) of staphylococcal nuclease (SNase) on fol d into a state (A state) in acidic solution of high NaCl concentration , that is. U-A --> A. The transition curve of U-A --> A induced by the increasing of NaCl concentration was superimposed with that induced b y the increasing of HCl concentration, indicating that the U-A --> A t ransition is induced by the chloride anion being inclined to bind on s om: parts of SNase molecules in A state. Circular dichroism (CD spectr a showed that A state has substantial secondary structure. Size exclus ion chromatography measurement indicated that A state is compact in vo lume. The A state on bind with 1-anilino-naphthalene-8-sulfonate (ANS) , a fluorescent probe for hydrophobicity. These results indicated that A state of SNaseR is a molten globule-like state. Besides, our result s showed that A state om be unfolded by guanidine hydrochloride (Gu . HCl), implying that the hydrophobic interaction between side chains in A state is responsible to its stabilization.