Comparison of inactivation and unfolding of yeast alcohol dehydrogenase during denaturation in urea solutions

It has been reported that inactivation occurs before noticeable conformational changes can be detected during the denaturation of a number of enzymes by denaturants. Therefore, Tsou suggested that the conformation of the enzyme active sites is more easily perturbed and hence more flexible than the molecule as a whole (Tsou, Trends in Biochemical Science, 1986, 11, 427-429; Tsou, Science, 1993, 262, 380-381). In this study, inactivation and unfolding of yeast alcohol dehydrogenase containing zinc ions in urea solutions of different concentrations are compared. The results show that much lower concentrations of urea are required to bring about inactivation than significant unfolding of the enzyme molecule. At the same urea concentration, inactivation rate is much faster than that of the unfolding of the enzyme molecule as a whole. The results suggest that active sites of yeast alcohol dehydrogenase containing zinc ions also display more conformational flexibility than the enzyme molecules as a whole.