Glutamine synthetase from Mycobacterium avium.

Area of Science:

• Microbiology
• Biochemistry

Background:

• Mycobacterium avium requires ammonia or glutamine as a nitrogen source.
• Understanding ammonia assimilation is key to M. avium physiology.

Purpose of the Study:

• To characterize the glutamine synthetase enzyme in M. avium.
• To investigate the physiological regulation of ammonia assimilation.

Main Methods:

• Purification of M. avium glutamine synthetase using streptomycin sulfate, ammonium sulfate precipitation, and affinity chromatography.
• Enzyme activity assays including transferase assay, determination of pH optimum and temperature.
• Analysis of enzyme properties like molecular weight, sedimentation coefficient, isoelectric point, and inhibition by methionine sulfoximine.
• Treatment with snake venom phosphodiesterase to assess adenylylation regulation.

Main Results:

• The M. avium glutamine synthetase exhibited a pH optimum of 6.4 and optimal activity between 50-60°C.
• Enzyme activity decreased with increasing ammonium chloride concentrations, showing environmental regulation.
• The enzyme's molecular weight (600,000) and sedimentation coefficient (19.5 S) were similar to other bacterial glutamine synthetases.
• Methionine sulfoximine inhibited enzyme activity, and phosphodiesterase treatment released AMP, indicating adenylylation-dependent regulation.

Conclusions:

• M. avium glutamine synthetase is regulated by adenylylation, a common mechanism in bacteria.
• The enzyme's activity is responsive to environmental nitrogen availability, impacting M. avium's nitrogen assimilation.
• Characterization provides insights into the biochemical pathways of this important pathogen.