The Hildebrand solubility parameters, cohesive energy densities and internal energies of 1-alkyl-3-methylimidazolium-based room temperature ionic liquids were determined by the intrinsic viscosity method and their dependencies on the length of the alkyl group analyzed.

Chlorella vulgaris was cultivated in wastewater discharged from a steel‐making plant with the aim of developing an economically feasible system to remove ammonia from wastewater and CO2 from flue gas simultaneously. Since no phosphorus compounds existed in wastewater, external phosphate (15·3–46·0 g m−3) was added to the wastewater. After adaptation to 5% (v/v) CO2, the growth of C. vulgaris was significantly improved at a typical concentration of CO2 in flue gas of 15% (v/v). Growth of C. vulgaris in raw wastewater was better than that in wastewater buffered with HEPES at 15% (v/v) CO2. CO2 fixation and ammonia removal rates were estimated as 26·0 g CO2 m−3 h−1 and 0·92 g NH3 m−3 h−1, respectively, when the alga was cultivated in wastewater supplemented with 46·0 g PO43 m−3 without pH control at 15% (v/v) CO2. © 1997 SCI.

The extremely thermoacidophilic archaeon Sulfolobus solfataricus utilizes D-glucose as a sole carbon and energy source through the non-phosphorylated Entner-Doudoroff pathway. It has been suggested that this micro-organism metabolizes D-gluconate, the oxidized form of D-glucose, to pyruvate and D-glyceraldehyde by using two unique enzymes, D-gluconate dehydratase and 2-keto-3-deoxy-D-gluconate aldolase. In the present study, we report the purification and characterization of D-gluconate dehydratase from S. solfataricus, which catalyses the conversion of D-gluconate into 2-keto-3-deoxy-D-gluconate. D-Gluconate dehydratase was purified 400-fold from extracts of S. solfataricus by ammonium sulphate fractionation and chromatography on DEAE-Sepharose, Q-Sepharose, phenyl-Sepharose and Mono Q. The native protein showed a molecular mass of 350 kDa by gel filtration, whereas SDS/PAGE analysis provided a molecular mass of 44 kDa, indicating that D-gluconate and Ni 2+ activated, whereas EDTA inhibited the enzyme. A metal analysis of the purified protein revealed the presence of one Co 2+ ion per enzyme monomer. Of the 22 aldonic acids tested, only D-gluconate served as a substrate, with K m = 0.45 mM and V max = 0.15 unit/mg of enzyme. From N-terminal sequences of the purified enzyme, it was found that the gene product of SSO3198 in the S. solfataricus genome database corresponded to D-gluconate dehydratase (gnaD). We also found that the D-gluconate dehydratase of S. solfataricus is a phosphoprotein and that its catalytic activity is regulated by a phosphorylation-dephosphorylation mechanism. This is the first report on biochemical and genetic characterization of D-gluconate dehydratase involved in the non-phosphorylated Entner-Doudoroff pathway.

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Dihydroxy-acid dehydratase (DHAD) is one of the key enzymes involved in the biosynthetic pathway of the branched chain amino acids. Although the enzyme has been purified and characterized in various mesophiles, including bacteria and eukarya, the biochemical properties of DHAD from hyperthermophilic archaea have not yet been reported. In this study we cloned, expressed in Escherichia coli, and purified a DHAD homologue from the thermoacidophilic archaeon Sulfolobus solfataricus, which grows optimally at 80 degrees C and pH 3. The recombinant S. solfataricus DHAD (rSso_DHAD) showed the highest activity on 2,3-dihydroxyisovalerate among 17 aldonic acids tested. Interestingly, this enzyme also displayed high activity toward d-gluconate and some other pentonic and hexonic sugar acids. The k(cat)/K(m) values were 140.3 mM(-1) s(-1) for 2,3-dihydroxyisovalerate and 20.0 mM(-1) s(-1) for d-gluconate, respectively. A possible evolutionary explanation for substrate promiscuity was provided through amino acid sequence alignments of DHADs and 6-phosphogluconate dehydratases from archaea, bacteria and eukarya.