Alkaline unfolding and salt-induced folding of aminoacylase at high pH.

The conformational changes of aminoacylase during unfolding at alkaline pH have been followed by fluorescence emission, circular dichroism (CD) and ultraviolet difference spectra. The results of comparison of inactivation and conformation show that much lower values of alkaline pH are required to bring about inactivation than significant conformational change of the enzyme molecule. At pH above 12, although the enzyme has been inactivated, the apparently fully unfolded enzyme retains some ordered secondary structure. At pH 12 by adding KCl, the relatively unfolded state of denatured enzyme changes into a compact conformational state by hydrophobic collapsing, but no new secondary structure is formed. On decreasing the pH from pH 12 to approximate neutrality, the unfolded enzyme also undertakes the similar conformational transition. It can be suggested that hydrophobic collapsed intermediate may be a general intermediate conformational state from alkaline unfolded state to native state.