A membrane-bound ATPase from Halobacterium halobium: purification and characterization.

Area of Science:

• Biochemistry
• Microbiology
• Molecular Biology

Background:

• Extremely halophilic archaebacteria, such as Halobacterium halobium, possess unique adaptations to survive in high-salt environments.
• Understanding the enzymes involved in energy metabolism, like ATPases, is crucial for elucidating these survival mechanisms.

Purpose of the Study:

• To identify and characterize a novel ATPase from the plasma membrane of Halobacterium halobium.
• To investigate the enzyme's properties, including its subunit composition, substrate specificity, and optimal conditions for activity.

Main Methods:

• Enzyme isolation and purification from the plasma membrane using alkaline EDTA treatment and chromatographic techniques.
• Determination of molecular weight, subunit composition, and kinetic parameters (Km, Ki).
• Assessment of enzyme activity under varying salt concentrations, pH, and in the presence of specific inhibitors.

Main Results:

• A novel ATPase was purified, with a native molecular weight of approximately 320,000 Da, likely composed of alpha2beta2 subunits.
• The enzyme hydrolyzed ATP and other nucleoside triphosphates, required divalent cations (Mn2+ optimal), and exhibited peak activity at pH 5.5-6 in high sulfate solutions.
• The ATPase was stable in high sulfate but inactivated by low salt concentrations or low temperatures, and was insensitive to azide and vanadate inhibitors.

Conclusions:

• The characterized ATPase possesses unusual properties, adapted to the halophilic lifestyle of Halobacterium halobium.
• This enzyme is the most probable candidate for the catalytic component of the halobacterial ATP synthase, differing from F0F1-ATPase/synthase.