INACTIVATION PRECEDES CHANGES IN ALLOSTERIC PROPERTIES AND CONFORMATION OF D-GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE AND FRUCTOSE-1,6-BISPBOSPHATASE DURING DENATURATION BY GUANIDINIUM CHLORIDE

It has been shown that inactivation of several enzymes precedes overal l conformational changes of the enzyme molecules as a whole during den aturation [Tsou (1993) Science, 262, 380-381]. However, the relation b etween inactivation, loss of allosteric properties of oligomeric enzym es and unfolding of the enzyme molecule during denaturation remain lit tle explored. These have now been compared for D-glyceraldehyde-3-phos phate dehydrogenase (GAPDH) and fructose-1,6-bisphosphatase (FruP(2)as e) during denaturation by guanidinium chloride (GdmCl). GAPDH is compl etely inactivated at 0.3 M GdmCl but at this GdmCl concentration it st ill binds NAD(+) with negative co-operativity. At 0.4 M GdmCl, inactiv ation of FruP(2)ase reaches completion whereas its allosteric properti es, including the heterotropic effect of AMP inhibition and K+ activat ion with positive co-operativity, are only partially affected. Much hi gher GdmCl concentrations are required to bring about unfolding of the overall structures of both enzymes.