Stability of acetylcholinesterase in guanidine hydrochloride solution

The irreversible unfolding of acetylcholinesterase (acetylcholine hydrolyase, EC 3.1.1.7) by guanidine hydrochloride was studied by difference spectral, circular dichroic, and enzyme activity measurements. At pH 7.0 and in 1.1 M denaturant solution, a conformational state in which enzyme is completely inactive was detected. It is identical to the native enzyme as far as sedimentation coefficient and molecular weight are concerned, but differs from the native molecule by a slight loss in secondary structure and by a small perturbation of aromatic residues. Acetylcholinesterase in concentrated guanidine hydrochloride solution containing beta-mercaptoethanol dissociates and exists as a random coil of molecular weight 68 000.