Relative Role of Anions and Cations in the Stabilization of Halophilic Malate Dehydrogenase
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- 作者：Christine Ebel ; Pierre Faou ; Blandine Kernel ; and Giuseppe Zaccai
- 刊名：Biochemistry
- 出版年：1999
- 出版时间：July 13, 1999
- 年：1999
- 卷：38
- 期：28
- 页码：9039 - 9047
- 全文大小：92K
- 年卷期：v.38,no.28(July 13, 1999)
- ISSN：1520-4995
文摘
Halophilic malate dehydrogenase unfolds at low salt, and increasing the salt concentrationstabilizes, first, the folded form and then, in some cases, destabilizes it. From inactivation and fluorescencemeasurements performed on the protein after its incubation in the presence of various salts in a largerange of concentrations, the apparent effects of anions and cations were found to superimpose. A largerange of ions was examined, including conditions that are in general not of physiological relevance, toexplore the physical chemistry driving adaptation to extreme environments. The order of efficiency ofcations and anions to maintain the folded form is, for the low-salt transition, Ca2+ 
Mg2+ > Li+ NH4+ Na+ > K+ > Rb+ > Cs+, and SO42- OAc- F- > Cl-, and for the high-salt transition,NH4+ Na+ K+ Cs+ > Li+ > Mg2+ > Ca2+, and SO42- OAc- F- > Cl- > Br- > I-. If acation or anion is very stabilizing, the effect of the salt ion of opposite charge is limited. Anions of highcharge density are always the most efficient to stabilize the folded form, in accordance with the orderfound in the Hofmeister series, while cations of high charge density are the most efficient only at thelower salt concentrations and tend to denature the protein at higher salt concentrations. The stabilizingefficiency of cations and anions can be related in a minor way to their effect on the surface tension of thesolution, but the interaction of ions with sites only present in the folded protein has also to be taken intoaccount. Unfolding at high salt concentrations corresponds to interactions of anions of low charge densityand cations of high charge density with the peptide bond, as found for nonhalophilic proteins.
Mg2+ > Li+ NH4+ Na+ > K+ > Rb+ > Cs+, and SO42- OAc- F- > Cl-, and for the high-salt transition,NH4+ Na+ K+ Cs+ > Li+ > Mg2+ > Ca2+, and SO42- OAc- F- > Cl- > Br- > I-. If acation or anion is very stabilizing, the effect of the salt ion of opposite charge is limited. Anions of highcharge density are always the most efficient to stabilize the folded form, in accordance with the orderfound in the Hofmeister series, while cations of high charge density are the most efficient only at thelower salt concentrations and tend to denature the protein at higher salt concentrations. The stabilizingefficiency of cations and anions can be related in a minor way to their effect on the surface tension of thesolution, but the interaction of ions with sites only present in the folded protein has also to be taken intoaccount. Unfolding at high salt concentrations corresponds to interactions of anions of low charge densityand cations of high charge density with the peptide bond, as found for nonhalophilic proteins.