Effects of guanidine hydrochloride on pyruvate dehydrogenase complex

Many molecules of pyruvate decarboxylase (E1) and dihydrolipoamide dehydrogenase (E3) bind non-covalently to a sixty-meric lipoate acetyltransferase (E2), forming the Bacillus stearothermophilus pyruvate dehydrogenase complex. Changes in the complex induced by incubation in guanidine hydrochloride (GdnHCl) solution and those induced by the incubation followed by removal of GdnHCl were examined. Small amount of GdnHCl induced reversible changes in the complex. The removal re-associated all components to the complex and restored the enzyme activities of the complex and its components. NaCl induced similar changes, and the effect of GdnHCl was implied as a salt rather than a denaturant. On the other hand, larger amount of GdnHCl induced irreversible changes in the complex. E1, E2, and E3 were dissociated and inactivated; FAD was released from E3. GdnHCl at concentrations limited to a small range around 1.0 M induced a partial and irreversible aggregation. The removal of GdnHCl yielded an E2-E3 complex (57S), restoring most activities of E2 and E3. Loss in enzyme activity of E1 might be responsible for that of the complex.