Halophilic adaptation of enzymes

It is now clear that the understanding of halophilic adaptation at a molecu lar level requires a strategy of complementary experiments, combining molec ular biology, biochemistry, and cellular approaches with physical chemistry and thermodynamics. In this review, after a discussion of the definition a nd composition of halophilic enzymes, the: effects of salt on their activit y, solubility, and stability are reviewed. We then describe how thermodynam ic observations, such as parameters pertaining to solvent-protein interacti ons or enzyme-unfolding kinetics, depend strongly on solvent composition an d reveal the important role played by water and ion binding to halophilic p roteins. The three high-resolution crystal structures now available for hal ophilic proteins are analyzed in terms of haloadaptation, and finally cellu lar response to salt stress is discussed briefly.