S-adenosylhomocysteine metabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways involving S-adenosylhomocysteine; the L-enantiomer is formed from S-adenosylmethionine and is a strong inhibitor of S-adenosylmethionine-mediated methylation reactions. It can be cleaved to form adenosine and homocysteine. [ISBN:0198506732]

S-adenosylhomocysteine (SAH) metabolic process is a crucial biochemical pathway involved in the regulation of various cellular functions. It centers around the synthesis and subsequent breakdown of SAH, a potent inhibitor of numerous methyltransferases.

The process begins with the synthesis of SAH from S-adenosylmethionine (SAM), a universal methyl donor in cellular metabolism. This reaction is catalyzed by methyltransferases, which utilize SAM as a substrate to transfer a methyl group to various molecules, including DNA, RNA, proteins, and lipids. The transfer of the methyl group converts SAM to SAH, which is a byproduct of this methylation reaction.

SAH is a potent inhibitor of most methyltransferases. It binds to the active sites of these enzymes, competing with SAM for binding and hindering their catalytic activity. This inhibition is crucial for maintaining the balance of methylation reactions in the cell.

To counter the accumulation of SAH and restore the activity of methyltransferases, the cell employs a specific pathway for SAH degradation. This process involves two key enzymes:
1. **SAH hydrolase**: This enzyme catalyzes the hydrolysis of SAH to homocysteine and adenosine, a reversible reaction.
2. **Methionine synthase**: This enzyme catalyzes the methylation of homocysteine to methionine, using 5-methyltetrahydrofolate as a methyl donor.

These reactions result in the regeneration of methionine, which is subsequently converted back to SAM by the enzyme **methionine adenosyltransferase (MAT)**. This completes the cycle, restoring the cellular pool of SAM and allowing for continued methylation reactions.

The SAH metabolic process is intricately linked to various cellular functions, including:
- **Gene regulation**: DNA methylation plays a vital role in gene regulation, and SAH levels influence this process.
- **Neurotransmitter synthesis**: SAH is involved in the synthesis of neurotransmitters, such as dopamine, serotonin, and norepinephrine.
- **Immune response**: SAH levels can impact the immune system, influencing inflammation and other responses.
- **Cell growth and proliferation**: SAH levels are tightly regulated during cell growth and proliferation, and imbalances can contribute to various diseases.

Disruptions in SAH metabolism can lead to various pathological conditions, including:
- **Cardiovascular disease**: Elevated SAH levels are associated with an increased risk of cardiovascular disease.
- **Neurodegenerative diseases**: SAH accumulation can contribute to neurodegenerative disorders, such as Alzheimer's disease.
- **Cancer**: Aberrant SAH metabolism can promote tumor growth and metastasis.

Therefore, understanding and regulating SAH metabolic processes is critical for maintaining cellular homeostasis and preventing various diseases.'
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Proteins (2)

Compounds (3)