Ferredoxin-dependent glutamate synthase: involvement in ammonium assimilation in Haloferax mediterranei

Glutamate synthase (GOGAT) is one of the two important enzymes involved in the ammonium assimilation pathway glutamine synthetase (GS)/GOGAT, which enables Hfx. mediterranei to thrive in media with low ammonium concentration or containing just nitrate as single nitrogen source. The gene coding for this enzyme, gltS, has been sequenced, analysed and compared with other GOGATs from different organisms from the three domains of life. According to its amino acid sequence, Hfx. mediterranei GOGAT displays high homology with those from other archaeal halophilic organisms and with the bacterial alpha-like subunit. Hfx. mediterranei GOGAT and GS expression was induced under conditions of ammonium restriction. The GOGAT protein was found to be a monomer with a molecular mass of 163.78 kDa, which is consistent with that estimated by gel filtration, 198 ± 30 kDa. The enzyme is highly ferredoxin dependent: activity was only observed with one of the two different 2Fe–2S ferredoxins chromatographically isolated from Hfx. mediterranei. The enzyme also displayed typical halophilic behaviour, being fully stable, and producing maximal activity, at salt concentrations from 3 to 4 M NaCl, pH 7.5 and a temperature of 50 °C.

Solubility, Density, Refractive Index, and Viscosity for the Polyhydric Alcohol + CsBr + H2O Ternary Systems at Different Temperatures

The solubility, density, refractive index, and viscosity data for the ethylene glycol + CsBr + H2O, 1,2-propanediol + CsBr + H2O, and glycerin + CsBr + H2O ternary systems have been determined at (288.15, 298.15, and 308.15) K. In all cases, the solubility of CsBr in aqueous solutions was decreased significantly due to the presence of polyhydric alcohol. The liquid–solid equilibrium experimental data were correlated using the NRTL (nonrandom two-liquid) activity coefficient model, considering nondissociation of the dissolved salt in the liquid phase, and new interaction parameters were estimated. The mean deviations between calculated and experimental compositions were low, showing the good descriptive quality and applicability of the NRTL model. The refractive indices, densities, and viscosities for the unsaturated solutions of the three ternary systems have also been measured at three temperatures. Values for all of the properties were correlated with the salt concentrations and proportions of polyhydric alcohol in the solutions.