| | 1 | Author
| FranciscoJ G M Urianaa, Marí, C. Alvarez-Ossorio3, Marí, M. Sánchez-Garcés3, FranciscoF. De, LaR. Osab, AngelM. Relimpio3 | Requires cookie* | | | Title
| Effect of Salt on the Activity and Stability of Aspartate Aminotransferase from the Halophilic Archaebacterium Haloferax mediterranei  | | | | Abstract
| The aspartate aminotransferase from Haloferax mediterranei, which is in the cell mainly as apoenzym e, requires high concentrations o f salt for both activity and stability. The maximum activity is reached with 3.5 m KC1 in the assay. The effect o f different cations and anions has been studied using several types o f salts. M onovalent cations show a significant difference in effectiveness o f promoting the activity with the follow ing order: K + > R b + > N a + > N H 4+. M g++ and polyvalent cations with organic character cause partial activity with maximum ef fectiveness at 0.1 m , an inhibition at higher concentration is observed. A nions, added as p otas sium salts, promote enzyme activity with the following order: Cl" > N 0 3~ > I " > SCN~. Like activity, the enzyme stability depends on salt concentrations. Incubation o f the enzyme with a low salt concentration leads to inactivation following pseudofirst order kinetics. The inactivat ed enzyme is partially reactivated by high concentrations o f KC1 follow ing second order kinet ics. Taking into account the dimeric structure o f this enzyme, high concentrations o f salt could stabilize the dimer, which is the active form. The salt effects on halophile aspartate am ino transferase are discussed considering hydrophobic and electrostatic interactions. | | | |
Reference
| Z. Naturforsch. 47c, 375 (1992); received December 17 1991 /February 21 1992 | | | |
Published
| 1992 | | | |
Keywords
| Halophilic Bacteria, Aspartate Aminotransferase, Salt Effects, Activity and Stability, H aloferax mediterranei | | | |
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| default:Reihe_C/47/ZNC-1992-47c-0375.pdf | | | | Identifier
| ZNC-1992-47c-0375 | | | | Volume
| 47 | |
| 2 | Author
| FranciscoJ. García-Murianaa, Marí, C. Alvarez-Ossorioa, Marí, M. Sánchez-Garcés3, FranciscoF. De La Rosab, AngelM. Relimpioa | Requires 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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| default:Reihe_C/50/ZNC-1995-50c-0241.pdf | | | | Identifier
| ZNC-1995-50c-0241 | | | | Volume
| 50 | |
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