Cystathionine β-synthase

Definition

Cystathionine β-synthase is an enzyme that catalyzes the condensation of homocysteine and serine to form cystathionine, which is a key step in the transsulfuration pathway. This pathway plays an important role in the metabolism of sulfur-containing amino acids and integrates closely with various metabolic pathways, particularly the citric acid cycle and one-carbon metabolism, affecting cellular homocysteine levels and glutathione synthesis.

5 Must Know Facts For Your Next Test

1. Cystathionine β-synthase requires pyridoxal phosphate (vitamin B6) as a cofactor for its enzymatic activity.
2. Deficiencies in cystathionine β-synthase can lead to homocystinuria, a disorder characterized by elevated levels of homocysteine in the blood.
3. The enzyme plays a significant role in the regulation of sulfur amino acid metabolism, linking it to both the citric acid cycle and the synthesis of important biomolecules.
4. Cystathionine β-synthase activity can be influenced by various factors, including genetic variations and nutritional status.
5. By converting homocysteine into cystathionine, this enzyme helps to prevent toxic accumulation of homocysteine and supports overall amino acid balance in cells.

Review Questions

• How does cystathionine β-synthase contribute to maintaining amino acid balance within the cell?
  • Cystathionine β-synthase plays a crucial role in the transsulfuration pathway by converting homocysteine into cystathionine. This process not only helps in regulating levels of homocysteine, which can be toxic if accumulated, but also provides cysteine for protein synthesis and glutathione production. By managing these amino acids, the enzyme supports cellular health and function.
• Discuss the implications of cystathionine β-synthase deficiency on human health, particularly in relation to cardiovascular disease.
  • A deficiency in cystathionine β-synthase leads to increased levels of homocysteine in the blood, known as homocystinuria. Elevated homocysteine is a recognized risk factor for cardiovascular diseases due to its potential to damage blood vessels and promote thrombus formation. This condition highlights the importance of cystathionine β-synthase in maintaining proper amino acid metabolism and reducing disease risk.
• Evaluate the interconnectedness of cystathionine β-synthase activity with other metabolic pathways, including the citric acid cycle and one-carbon metabolism.
  • Cystathionine β-synthase serves as a pivotal point where sulfur amino acid metabolism intersects with other metabolic pathways. Its activity influences levels of homocysteine and consequently impacts one-carbon metabolism by providing substrates for folate-dependent reactions. Additionally, through the production of cysteine from homocysteine, it feeds into processes linked to the citric acid cycle via acetyl-CoA. This interconnectedness underscores its vital role in integrating various metabolic functions within the cell.

Related terms

Homocysteine: An amino acid that is a product of methionine metabolism and can contribute to cardiovascular diseases if present at elevated levels.

Transsulfuration Pathway: A metabolic pathway that converts homocysteine into cysteine through the intermediate formation of cystathionine, utilizing enzymes like cystathionine β-synthase.

Glutathione: A powerful antioxidant made from cysteine, glutamate, and glycine, crucial for protecting cells from oxidative damage and maintaining redox homeostasis.