High concentrations of D-glyceraldehyde-3-phosphate dehydrogenase stabilize the enzyme against denaturation by low concentrations of GuHCl

It is known that denaturation of D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) in low concentrations of GuHCl, around 0.5 M, at 25 d egrees C, leads first to a burst phase drop of activity, followed by slow u nfolding with further loss of enzyme activity and aggregation. However, GAP DH at higher concentrations does not increase the aggregation in the slow p hase as would be expected but decreases both the inactivation and aggregati on of the enzyme instead. It seems that GAPDH at high concentrations protec ts the enzyme against GuHCl-denaturation. This protection is not a general effect of GuHCl binding by increased protein concentration but specific for GAPDH, as either bovine serum albumin or alpha-lactalbumin does not show a ny protection at similar concentrations. It is proposed that dissociation o f tetrameric GAPDH into dimers in the early phase of denaturation in dilute GuHCl is reversible and further unfolding of the dimer to an aggregation p rone species is irreversible and rate-limiting for the unfolding process. H igh concentrations of the enzyme shift the equilibrium towards the tetramer thus decrease the aggregation of GAPDH in dilute GuHCl. (C) 2000 Elsevier Science B.V. All rights reserved.