Subunit dissociation and unfolding of bovine liver glutamate dehydrogenase induced by guanidine hydrochloride.

Equilibrium and kinetic measurements were carried out on the denaturation of bovine liver glutamate dehydrogenase (L-glutamate:NAD(P)+ oxidoreductase (deaminating), EC 1.4.1.3) induced by guanidine hydrochloride (Gdn-HCl) in 0.2 M phosphate buffer (pH 7.3) using two types of detection, light-scattering and circular dichroism. The results obtained in equilibrium studies showed that the enzyme exists in solution as hexamers of native subunit at Gdn-HCl concentrations below 0.6 M, as trimers of native subunit in the concentration range between 1.0 and 2.0 M, and as monomers with unfolded structure above 2.8 M. From the kinetic studies, it was found that the dissociation of hexamer to trimer takes place more rapidly than that of trimer to monomer by a factor of 10, and it was also found that the unfolding of the polypeptide chain occurs much more slowly than subunit dissociation.