stability studies on maize leaf phosphoenolpyruvate carboxylase the effect of salts the solution stability of phosphoenolpyruvate carboxylase pepc has been determined in the presence of various salts by temperatureaccelerated enzyme inactivation and also by using highperformance sizeexclusion chromatography kosmotropic water structuring anions in the hofmeister series hpo42 citrate3 so42 f oac and glutamate stabilized the enzyme most effectively while cl a borderline hofmeister anion and br a chaotropic anion were destabilizing the effects of the cations on pepc stability ranged from relatively inert na k to destabilizing ch34n nh4 li the observed stabilization of pepc by specific salts has been interpreted in terms of the positive surface tension increment and the waterstructuring effects conferred on the solution by the specific stabilizing reagents both these effects enhance hydrophobic interactions of proteins and increase the energy required to enlarge the surface area of the solvent cavity in which the protein resides the destabilization of pepc by some salts at a concentration of 05 m was associated with the dissociation of the tetrameric enzyme into its dimeric and monomeric forms a process most probably occurring as a result of ionpeptide dipole binding which promotes proteinsolvent interaction and a subsequent reduction in the free energy of cavity formation the stabilization of enzyme activity by kosmotropic salts depended on the salt concentration with maximum stabilization of pepc in solution at 52 degrees c observed with 0608 m sodium glutamate 2 m kf and 22 m koac higher concentrations of these salts resulted in decreased activity this reduction in activity of pepc in the presence of high concentrations of kosmotropic salts appears to be associated with irreversible conformational changes of the tetrameric enzyme