Conformational changes in pantetheine hydrolase as a function of guanidinium chloride concentration

The denaturation of pantetheinase (pantetheine hydrolase, EC 3.5.1.-) was followed in guanidinium chloride using tyrosyl and tryptophanyl residues as probes in connection with change in enzymatic activity. Movements of tryptophanyl and tyrosyl residues during denaturation were studied by second-derivative and fluorescence spectroscopy and the number of these amino acids present in the protein was calculated from spectroscopic data. Pantetheinase shows a very high resistance to denaturation, being completely unfolded at guanidinium chloride concentration higher than 6.5 M. Monitoring enzymatic activity shows that inactivation of the enzyme occurred before noticeable conformational changes were detected and it is suggested that the conformation of the active site is flexible and easily perturbable compared to the protein as a whole. This inactivation is reversible, as shown by renaturation experiments. Second-derivative and fluorescence spectra showed also that tyrosyl and tryptophanyl residues are largely exposed in the native protein, confirming its hydrophobic behavior.