Effects of Low Concentrations of Guanidine . HCl on the Reconstitution of Lactic Dehydrogenase from Pig Muscle in vitro. Evidence for Guanidine Binding to the Native Enzyme

Abstract

The presence of low concentrations of guanidine.cntdot.HCl has a pronounced effect on the overall rate of reactivation of lactic dehydrogenase from pig muscle after preceding dissociation and deactivation in various denaturants. The observed attenuation is a function of the amount of guanidine.cntdot.HCl present during reconstitution. At a given guanidine concentration in the reactivation buffer the yield, but not the rate of reactivation, is influenced by the extent of denaturation caused initially in the process of deactivation and dissociation. As a possible explanation for the influence of guanidine.cntdot.HCl on the kinetics of reconstitution, binding of the ligand to intermediates of folding and association is considered. This hypothesis is corroborated by the observation that guanidine.cntdot.HCl in the relevant concentration range does bind to native lactic dehydrogenase without inactivating the enzyme or disrupting its quaternary structure. A kinetic model comprising guanidine binding to both the native enzyme and structural intermediates is proposed to describe the observed effects of guanidine.cntdot.HCl on the rate of reactivation. In addition, the Kd for guanidine binding to intermediates of reconstitution and to native lactic dehydrogenase are estimated.