Halophilic malate dehydrogenase--a case history of biophysical investigations: ultracentrifugation, light-, X-ray- and neutron scattering.

Halophilic malate dehydrogenase (hMDH) from Haloarcula marismortui has been isolated, purified and characterized by biochemical and biophysical solution studies. A stabilization mechanism at extremely high concentrations of salt, based on the formation of co-operative hydrate bonds between the protein and hydrated salt ions, was suggested from thermodynamic analysis of native enzyme solutions. Recently the gene coding for hMDH was isolated and sequenced and an active enzyme cloned (F. Cendrin, J. Chroboczek, G. Zaccai, H. Eisenberg and M. Mevarech, unpublished work). A study of the crystal structure of hMDH in a high-salt physiological medium is in progress (O. Butbul-Dym & J. Sussman, personal communication). Here we discuss in depth implications of these recent developments on our earlier results.