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Chick brain glutamine synthetase and Mn2+-Mg2+ interactions
1Laboratoire de Microbiologie, Université Louis Pasteur, Strasbourg, France.
Neurochemical Research
|November 1, 1987
Summary
Chick brain glutamine synthetase (GS) was purified and characterized as an octamer. Its activity is regulated by specific cations like Mg2+, Co2+, and Mn2+, suggesting intracellular control mechanisms.
Area of Science:
- Biochemistry
- Neuroscience
- Enzymology
Background:
- Glutamine synthetase (GS) is a crucial enzyme in amino acid metabolism.
- Understanding GS structure and regulation is vital for comprehending brain function.
Purpose of the Study:
- To purify and characterize glutamine synthetase (GS) from chick brain.
- To investigate the effects of various cations on GS activity and explore potential regulatory mechanisms.
Main Methods:
- Enzyme purification using ammonium sulfate fractionation, affinity chromatography, electrofocusing, and Sephadex G-150 chromatography.
- Molecular weight determination via sedimentation equilibrium and gel electrophoresis.
- Enzyme activity assays with different cations (Mg2+, Co2+, Mn2+) and ATP.
Main Results:
- Purified chick brain GS is an octamer with a subunit molecular weight of 45,000 and native molecular weight of 364,000.
- GS exists in monomer, tetramer, and octamer forms in the presence of Mg2+.
- Mg2+, Co2+, and Mn2+ activate GS activity, with Mg2+ being the most potent activator. Mn2+ exhibits concentration-dependent effects, with narrow optimal ranges and inhibition at higher concentrations.
Conclusions:
- Chick brain GS possesses a complex oligomeric structure regulated by divalent cations.
- A regulatory system involving Mn2+ modulating Mg2+-dependent GS activity is proposed.
- These cation interactions are significant for the intracellular control of glutamine synthesis in the brain.