The conformational change of Escherichia coli alkaline phosphatase in different denaturants during unfolding is monitored by phosphorescence lifetime of tryptophan (Trp) residue. The results suggest that addition of different denaturants to solution of protein results in a major change of microenvironment near Trp residues, causing a decrease of the phosphorescence emission and a corresponding shortening of the phosphorescence lifetimes. The results predict that the Trp residues are transferred from rigid hydrophobic core to the surface of protein. The data of thermodynamic parameters such as activation energy, activation entropy (△S°) and activation enthalpy (△H°) are obtained by the Arrhenius plots of AP, which further confirm that there is a stable intermediate state between the folding and unfolding conformation in AP solution.

Key words: ESCHERICHIA COLI, PHOSPHOKINASE, TRYPTOPHAN, PROTEIN, CONFORMATION, ACTIVATION ENERGY