thymine catabolic process
Definition
Target type: biologicalprocess
The chemical reactions and pathways resulting in the breakdown of thymine, 5-methyluracil, one of the two major pyrimidine bases present (as thymidine) in DNA but not found in RNA other than (as ribothymidine) in transfer RNA, where it is a minor base. [GOC:go_curators]
Thymine catabolism is the metabolic pathway that breaks down thymine, a pyrimidine base found in DNA. This process is crucial for recycling nucleotides and preventing the buildup of potentially harmful byproducts. Here's a detailed breakdown:
1. **Thymine Deamination:** The first step involves the conversion of thymine into uracil by the enzyme thymine DNA glycosylase (TDG). This enzyme removes thymine from DNA and replaces it with uracil. Uracil is a normal component of RNA, but not DNA.
2. **Uracil Degradation:** Uracil is further degraded through a series of enzymatic reactions:
* **Dihydropyrimidine dehydrogenase (DPD)** catalyzes the reduction of uracil to dihydrouracil.
* **Dihydrouracil dehydrogenase (DHD)** oxidizes dihydrouracil to β-ureidopropionate.
* **β-Ureidopropionase** hydrolyzes β-ureidopropionate into β-alanine and carbamoyl phosphate.
3. **β-alanine Metabolism:** β-alanine is further metabolized through the following steps:
* **β-Alanine:pyruvate transaminase** converts β-alanine to malonic semialdehyde.
* **Malonic semialdehyde dehydrogenase** oxidizes malonic semialdehyde to malonyl-CoA.
* Malonyl-CoA is a key intermediate in fatty acid biosynthesis.
4. **Carbamoyl Phosphate Metabolism:** Carbamoyl phosphate is a key intermediate in the biosynthesis of pyrimidines and arginine.
The thymine catabolic pathway is essential for maintaining the integrity of DNA and recycling nucleotides. Defects in these enzymes can lead to a buildup of uracil in DNA, which can result in mutations and other genetic instabilities. Additionally, these enzymes are involved in various metabolic processes, including the biosynthesis of pyrimidines and arginine. The degradation of thymine also plays a role in maintaining the balance of nitrogenous bases in the body.'
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Proteins (1)
| Protein | Definition | Taxonomy |
|---|---|---|
| Dihydropyrimidine dehydrogenase [NADP(+)] | A dihydropyrimidine dehydrogenase [NADP(+)] that is encoded in the genome of human. [PRO:DNx, UniProtKB:Q12882] | Homo sapiens (human) |
Compounds (4)
| Compound | Definition | Classes | Roles |
|---|---|---|---|
| eniluracil | eniluracil: structure in first source; inactivates dihydropyrimidine dehydrogenase | pyrimidone | |
| 5-iodouracil | 5-iodouracil : An organoiodine compound consisting of uracil having an iodo substituent at the 5-position. 5-iodouracil: RN given refers to parent cpd | organoiodine compound | antimetabolite |
| 5-cyanouracil | |||
| 5-vinyluracil | 5-vinyluracil: RN given refers to unlabeled parent cpd |