Abstract
This is the first experimental evidence of an equilibrium intermediate in the unfolding of triosephosphate isomerase (TIM). The reversible unfolding of S. cerevisiae TIM induced by both guanidine HCl (Gdn-HCl) and urea, are apparently monophasic when followed by spectroscopic techniques. Kinetic analysis and ANS binding data confirm a two-state transition in urea. nevertheless, in Gdn-HCl they indicate an intermediate. Hydrodynamic properties of the intermediate are consistent with a compact monomer.