Open AccessSpectopotentiometric properties and salt‐dependent thermotolerance of a [2Fe–2S] ferredoxin‐involved nitrate assimilation in Haloferax mediterranei
Author(s) -
MartínezEspinosa Rosa María,
Richardson David J.,
Butt Julea N.,
Bonete María José
Publication year - 2007
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.2007.00942.x
Subject(s) - ferredoxin , halophile , haloarchaea , nitrate , thermostability , chemistry , nitrite , iron–sulfur cluster , ferredoxin thioredoxin reductase , salt (chemistry) , inorganic chemistry , archaea , biochemistry , biology , enzyme , thioredoxin , bacteria , organic chemistry , thioredoxin reductase , gene , genetics
Haloferax mediterranei is a halophilic archaeon that can grow using nitrate as the sole nitrogen source. A ferredoxin that serves as the physiological electron donor to the nitrate and nitrite reductases in this assimilatory process has been characterized. The ferredoxin was found to contain approximately two atoms of iron and two atoms of sulphur, indicative of the binding of a [2Fe–2S] cluster. The electron paramagnetic resonance spectrum of the reduced form of the protein displayed a rhombic signal, with g x =1.91, g y =1.98, g z =2.07, that shows considerable similarity to plant and algal [2Fe–2S] ferredoxins. UV‐visible spectropotentiometric analysis determined a midpoint redox potential for the [2Fe–2S] 2+/1+ transition of around −285 mV vs. SHE that was independent of salt concentration. UV‐visible spectroscopy was also used to establish that the [2Fe–2S] cluster integrity of this protein was maintained over the pH range 5–11. Significantly, the Haloferax mediterranei ferredoxin was shown to be a highly thermostable protein. It was stable up to 60 °C in a low‐salt (0.2 M) medium and this increased to 80 °C in a high‐salt (4 M) medium. This thermostability at high salt concentration is an essential physiological characteristic because haloarchaea are mainly found in environments where high temperatures and concentrated salt water occur.