Effect of Salt on the Activity and Stability of Aspartate Aminotransferase from the Halophilic Archaebacterium Haloferax mediterranei

Muriana, Francisco J.G.; Alvarez-Ossorio, María C.; Sánchez-Garcés, María M.; Rosa, Francisco F. de la; Relimpio, Angel M.

doi:10.1515/znc-1992-0610

Cited by 7 publications

(3 citation statements)

References 11 publications

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“…However, an immediate and irreversible loss of activity was observed when the protein was dialyzed into divalent salts such as 2 M MgCl 2 or CaCl 2 . This finding is in agreement with those for other enzymes from halophiles and awaits a satisfactory explanation (28,34). Monovalent salt stabilization of halo-philic, negatively charged enzymes is generally believed to consist of two components (27).…”

Section: Resultssupporting

confidence: 88%

Purification and characterization of a mesohalic catalase from the halophilic bacterium Halobacterium halobium

Brown‐Peterson

Salin

1995

J Bacteriol

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When subjected to the stress of growth in a relatively low-salt environment (1.25 M NaCl), the halophilic bacterium Halobacterium halobium induces a catalase. The protein has been purified to electrophoretic homogeneity and has an M(r) of 240,000 and a subunit size of approximately 62,000. The enzyme is active over a broad pH range of 6.5 to 10.0, with a peak in activity at pH 7.0. It has an isoelectric point of 4.0. This catalse, which is not readily reduced by dithionite, shows a Soret peak at 406 nm. Cyanide and azide inhibit the enzyme at micromolar concentrations, whereas maleimide is without effect. The addition of 20 mM 3-amino-1,2,4-triazole results in a 33% inhibition in enzymatic activity. The tetrameric protein binds NADP in a 1:1 ratio but does not peroxidize NADPH, NADH, or ascorbate. Although the enzymatic activity is maximal when assayed in a 50 mM potassium phosphate buffer with no NaCl, prolonged incubation in a buffer lacking NaCl results in inactive enzyme. Moreover, purification must be performed in the presence of 2 M NaCl. Equally as effective in retaining enzymatic function are NaCl, LiCl, KCl, CsCl, and NH4Cl, whereas divalent salts such as MgCl2 and CaCl2 result in the immediate loss of activity. The catalase is stained by pararosaniline, which is indicative of a glycosidic linkage. The Km for H2O2 is 60 mM, with inhibition observed at concentrations in excess of 90 mM. Thus, the mesohalic catalase purified from H. halobium seems to be similar to other catalases, except for the salt requirements, but differs markedly from the constitutive halobacterial hydroperoxidase.

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Section: Resultssupporting

confidence: 88%

Purification and characterization of a mesohalic catalase from the halophilic bacterium Halobacterium halobium

Brown‐Peterson

Salin

1995

J Bacteriol

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“…Molecular nitrogen is generally the main product, but formation has also been observed in several species Hochstein and Tomlinson, 1985;Mancinelli and Hochstein, 1986;Tomlinson et al, 1986). The dissimilatory nitrate reductases of Haloferax denitrificans and Haloferax mediterranei have been characterized (Alvarez-Ossorio et al, 1992;Hochstein, 1991;Hochstein and Lang, 1991). Analysis of nitrate respiration-deficient mutants of Haloferax volcanii has enabled the genetic identification of three ABC transporters as essential elements of nitrate respiration.…”

Section: Dissimilatory Biochemical Pathwaysmentioning

confidence: 99%

Halophilic Microorganisms and their Environments

Oren

2002

Cellular Origin, Life in Extreme Habitats and Astrobiology

404

294

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“…In an earlier report we described the purification of the halophilic aspartate aminotransferase (EC 2.6.1.1; AspAT) from Haloferax mediterranei, which not only tolerates salt for its stability, but also requires a high salt concentration for its activity [9][10][11][12][13]. This halophilic transaminase is a dimeric enzyme containing identical subunits; its coenzyme is weakly bound at each active site (Kd approx.…”

Section: Introductionmentioning

confidence: 99%

Further thermal characterization of an aspartate aminotransferase from a halophilic organism

Muriana

Alvarez-Ossorio

Relimpio

1994

Biochemical Journal

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Aspartate aminotransferase (AspAT, EC 2.6.1.1) from the halophilic archaebacterium Haloferax mediterranei was purified [Muriana, Alvarez-Ossorio and Relimpio (1991) Biochem. J. 278, 149-154] and further characterization of the effects of temperature on the activity and stability of the halophilic AspAT were carried out. The halophilic transaminase is most active at 65 degrees C and stable at high temperatures, under physiological or nearly physiological conditions (3.5 M KCl, pH 7.8). Thermal inactivation (60-85 degrees C) of the halophilic AspAT followed first-order kinetics, 2-oxoglutarate causing a shift of the thermal inactivation curves to higher temperatures. The salt concentration affected the thermal stability of the halophilic transaminase at 60 degrees C, suggesting that disruption of hydrophobic interactions may play an important role in the decreased thermal stability of the enzyme.

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Effect of Salt on the Activity and Stability of Aspartate Aminotransferase from the Halophilic Archaebacterium Haloferax mediterranei

Cited by 7 publications

References 11 publications

Purification and characterization of a mesohalic catalase from the halophilic bacterium Halobacterium halobium

Purification and characterization of a mesohalic catalase from the halophilic bacterium Halobacterium halobium

Halophilic Microorganisms and their Environments

Further thermal characterization of an aspartate aminotransferase from a halophilic organism

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