Citrate synthase

Definition

Citrate synthase is an essential enzyme that catalyzes the first step of the citric acid cycle (Krebs cycle) by facilitating the condensation of acetyl-CoA and oxaloacetate to form citrate. This reaction is crucial as it marks the entry point for carbon skeletons into the cycle, linking carbohydrate, fat, and protein metabolism to energy production. Understanding citrate synthase provides insight into metabolic pathways and how energy is generated and regulated in living organisms.

5 Must Know Facts For Your Next Test

1. Citrate synthase is a homodimeric enzyme, meaning it consists of two identical subunits that work together to catalyze the reaction.
2. The reaction catalyzed by citrate synthase is irreversible and highly regulated, making it a key control point in cellular respiration.
3. This enzyme requires the presence of certain cofactors, such as magnesium ions (Mg²⁺), which assist in stabilizing substrates during the reaction.
4. Citrate synthase activity can be influenced by various metabolites, including NADH and ATP, which indicate the energy status of the cell.
5. Defects or malfunctions in citrate synthase have been linked to various metabolic disorders, highlighting its importance in maintaining metabolic balance.

Review Questions

• How does citrate synthase link different metabolic pathways within the cell?
  • Citrate synthase connects carbohydrate, fat, and protein metabolism by using acetyl-CoA derived from these macromolecules to produce citrate, the first intermediate in the Krebs cycle. This integration allows for a unified pathway where various nutrients can be converted into usable energy. The enzyme's activity ensures that the cell can efficiently utilize different energy sources depending on availability.
• What regulatory mechanisms affect citrate synthase activity and why are they important?
  • Citrate synthase is regulated by various metabolites such as NADH and ATP, which serve as indicators of the cell's energy status. When energy levels are high, these molecules inhibit citrate synthase activity to prevent overproduction of citrate, which could lead to metabolic imbalance. Conversely, when energy levels are low, citrate synthase is activated to promote ATP production through enhanced entry into the Krebs cycle. This regulatory feedback loop is vital for maintaining cellular homeostasis.
• Evaluate the impact of citrate synthase dysfunction on cellular metabolism and potential health implications.
  • Dysfunction in citrate synthase can severely disrupt cellular metabolism by impairing the Krebs cycle's efficiency. This can lead to reduced ATP production and an accumulation of intermediates, affecting overall metabolic balance. Such dysfunction has been linked to various metabolic disorders like diabetes and obesity, as well as certain cancers where altered energy production pathways are often observed. Understanding these implications underscores the enzyme's crucial role in health and disease.

Related terms

Krebs cycle: A series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

acetyl-CoA: A key molecule in metabolism that serves as a substrate for citrate synthase, produced from carbohydrates, fats, and proteins.

oxaloacetate: A four-carbon molecule that reacts with acetyl-CoA to form citrate in the first step of the citric acid cycle.