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'Haloferax mediterranei' in keywords Facet   section ZfN Section C  [X]
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1995 (1)
1992 (1)
1Author    M. Aria, C. Alvarez-Ossorioa, FranciscoJ G M Uriana3, FranciscoF. De La Rosab, AngelM. RelimpioaRequires cookie*
 Title    Purification and Characterization of Nitrate Reductase from the Halophile Archaebacterium Haloferax mediterranei  
 Abstract    Nitrate reductase is induced in cells o f H aloferax mediterranei by the presence o f nitrate upon anaerobic conditions. This enzyme was purified more than 35-fold with a yield o f 49%. Densitograms o f polyacrylamide gel electrophoresis show the preparation to be 85% purity. The best enzyme preparation has a specific activity o f 13.6 U /m g protein. It is the first halo­ philic nitrate reductase that has been purified near to homogeneity. The purification consists o f five steps: an amm onium sulphate precipitation and four successive gel chromatographies with Sepharose C L -4B, calcium phosphate, D EAE-Sephacel and Sephacryl S-200. An average Mr o f 170,000 was estimated by gel chromatography and non-denaturing gel electrophoresis. Effectiveness o f electron donors, cofactors and inhibitors are reported. At low salt concentra­ tion the halophilic nitrate reductase was inactivated follow ing first-order kinetics. The K m for nitrate depends on salt concentration and shows values in the range from 2.5 to 6.7 m M . 
  Reference    Z. Naturforsch. 47c, 670—6 (1992); received April 7/June 15 1992 
  Published    1992 
  Keywords    Halophilic Nitrate Reductase, Enzyme Purification, Enzyme Characterization, Haloferax mediterranei 
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 TEI-XML for    default:Reihe_C/47/ZNC-1992-47c-0670.pdf 
 Identifier    ZNC-1992-47c-0670 
 Volume    47 
2Author    FranciscoJ. García-Murianaa, Marí, C. Alvarez-Ossorioa, Marí, M. Sánchez-Garcés3, FranciscoF. De La Rosab, AngelM. RelimpioaRequires cookie*
 Title    Further Characterization of Aspartate Aminotransferase from Haloferax mediterranei: Pyridoxal Phosphate as Coenzyme and Inhibitor  
 Abstract    The enzyme aspartate aminotransferase has been isolated from the halophilic bacterium Haloferax mediterranei in its apoenzyme form. The interaction with its coenzyme (pyridoxal phosphate) has been investigated. For concentrations up to 0.05 mM, the incubation with pyridoxal phosphate reconstituted the active complex (holoenzyme) following a second order kinetic with a k2 of 5.2 min'mM"1. This active complex showed a dissociation constant (/Cd) of 7.8 x 10~6 m . For concentrations higher than 0.1 mM, pyridoxal phosphate produced an inactivation process with a complex second order kinetic. This inactivation is partially re­ verted by dialysis or by lysine treatment. Thus, after 80% of inactivation, 55% of the original activity is recovered by a long-time dialysis, and with 50 mM lysine also a partial reactivation (among 20-33%) is observed. The enzyme treated with 1 mM pyridoxal phosphate has a different behavior in Sepharose chromatography indicating that the modified enzyme pre­ sents a smaller size due to a conformational change. 
  Reference    Z. Naturforsch. 50c, 241—247 (1995); received October 4/November 4 1994 
  Published    1995 
  Keywords    Halophilic Bacteria, Aspartate Aminotransferase, PLP Effects, Activity and Stability, Haloferax mediterranei 
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 TEI-XML for    default:Reihe_C/50/ZNC-1995-50c-0241.pdf 
 Identifier    ZNC-1995-50c-0241 
 Volume    50