Abstract
Quantitative correlation between the variation of surface net and local hydrophobicities and the conformational change of cytochrome c induced by added acid and salts was investigated by using aqueous two-phase partitioning systems (ATPS). Cytochrome c is unfolded at pH 2 under conditions of low ionic strength, but it is refolded to the molten-globule state by further addition of acid. By addition of salts, a conformational change from the unfolded to the molten-globule state by the anion binding to the positive charge of a protein was also observed. Surface net and local hydrophobicities observed by using the ATPS method clearly show significant differences in these three conformational states, in contrast to the conventional CD measurement. The local hydrophobicity, which can be evaluated by the increment of partition coefficient by the binding of Triton added to the ATPS, is greatest for the molten-globule state, whereas its surface net hydrophobicity is intermediate between the unfolded and native states.
