Questions and Answers
What molecule is the starting point for the synthesis of glutamate, glutamine, proline, and arginine?
What significantly affects the concentration of α-ketoglutarate in cells?
Which enzyme starts the Citric Acid Cycle and is inhibited by α-ketoglutarate?
Which regulatory mechanism does NOT control glutamine synthetase?
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How does the concentration of ammonia affect the specific activity of glutamine synthetase?
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What form of glutamine synthetase (GS) is considered fully active?
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What role do divalent cations play in the regulatory mechanisms of glutamine synthetase?
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Which of the following is NOT a mechanism for the regulation of glutamine synthetase?
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Study Notes
α-Ketoglutarate as a Precursor
- α-Ketoglutarate is an intermediate in the Citric Acid Cycle, crucial for synthesizing amino acids such as glutamate, glutamine, proline, and arginine.
- Its concentration is influenced by cellular metabolism and enzymatic activity regulation.
Enzyme Regulation in E. coli
- Citrate synthase in E. coli initiates the Citric Acid Cycle and is inhibited by α-ketoglutarate through feedback inhibition.
- Additionally, the enzyme is affected by high ATP levels and DPNH.
Glutamate Synthesis Control
- The synthesis of glutamate from α-ketoglutarate is regulated by the Citric Acid Cycle and depends on reactant concentrations due to reversible transamination and glutamate dehydrogenase reactions.
Conversion to Glutamine
- Glutamate's conversion to glutamine is mediated by glutamine synthetase (GS), a central player in nitrogen metabolism.
- GS regulation involves:
- Repression and activation based on nitrogen availability.
- Enzymatic forms (taut and relaxed) influencing activity.
- Cumulative feedback inhibition from end product metabolites.
- Modifications via adenylation and deadenylation.
Nitrogen Availability Impact
- In nitrogen-rich environments or high ammonia conditions, GS levels are low.
- In low ammonia conditions, GS activity can increase by up to 20-fold.
Enzyme Conformation
- GS exists in two conformational states: taut (fully active) and relaxed (inactive).
- Removal of manganese shifts GS from taut to relaxed form, influencing its enzymatic activity.
Feedback Inhibition Mechanisms
- Cumulative feedback inhibition of GS occurs with a combination of various metabolites, including:
- L-tryptophan
- L-histidine
- AMP
- CTP
- Glucosamine-6-phosphate
- Carbamyl phosphate
- Alanine and glycine
- No single metabolite solely inhibits GS; instead, an accumulation of multiple metabolites exerts strong inhibition.
Adenylation and Regulatory Interaction
- GS activity can also be inhibited through adenylation, performed by the bifunctional adenylyltransferase/adenylyl removal (AT/AR) enzyme.
- Glutamine and a regulatory protein, PII, work together to promote adenylation of GS.
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Description
Explore the biochemical pathways involved in the synthesis of amino acids such as glutamate, glutamine, proline, and arginine from α-ketoglutarate. Understand the role of α-ketoglutarate in the Citric Acid Cycle and its regulation in E. coli. This quiz will test your knowledge of enzymatic activity and feedback inhibition in metabolic processes.
