Salt-dependent studies of NADP-dependent isocitrate dehydrogenase from the halophilic archaeon Haloferax volcanii

The salt-dependent stability of recombinant dimeric isocitrate dehydrogenase [ICDH; isocitrate: NADP oxidoreductase (decarboxylating), EC 1.1.1.42] from the halophilic archaeon Haloferax volcanii (Hv) was investigated in various conditions. Hv ICDH dissociation/deactivation was measured to probe the respective effect of anions and cations on stability. Surprisingly, enzyme stability was found to be mainly sensitive to cations and very little (or not) sensitive to anions. Divalent cations induced a strong shift of the active/inactive transition towards low salt concentration. A high resistance of Hv ICDH to chemical denaturation was also found. The data were analysed and are discussed in the framework of the solvation stability model for halophilic proteins.