L-cysteine catabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways resulting in the breakdown of L-cysteine, the L-enantiomer of 2-amino-3-mercaptopropanoic acid, i.e. (2R)-2-amino-3-mercaptopropanoic acid. [GOC:jsg, GOC:mah]

L-cysteine catabolism is a fundamental metabolic pathway responsible for the breakdown of the sulfur-containing amino acid L-cysteine. This process plays a vital role in cellular metabolism, detoxification, and the biosynthesis of essential molecules. The catabolism of L-cysteine proceeds through two main pathways: the transsulfuration pathway and the cysteine dioxygenase pathway.

**1. Transsulfuration Pathway:**

* **Step 1: Conversion to cystathionine:** L-cysteine reacts with α-ketoglutarate in a reaction catalyzed by the enzyme cystathionine β-synthase. This reaction produces cystathionine, a sulfur-containing amino acid.
* **Step 2: Conversion to homocysteine:** Cystathionine is then cleaved by cystathionine γ-lyase, releasing homocysteine, α-ketobutyrate, and hydrogen sulfide (H2S).
* **Step 3: Conversion to methionine:** Homocysteine can be remethylated to methionine, another essential amino acid. This reaction requires the enzyme tetrahydrofolate reductase (THF reductase) and the coenzyme tetrahydrofolate (THF).

**2. Cysteine Dioxygenase Pathway:**

* **Step 1: Oxidation to cysteine sulfinate:** L-cysteine is oxidized to cysteine sulfinate by the enzyme cysteine dioxygenase. This reaction requires molecular oxygen (O2) and generates hydrogen peroxide (H2O2).
* **Step 2: Conversion to sulfite:** Cysteine sulfinate is then decarboxylated by the enzyme cysteine sulfinate decarboxylase, producing sulfite and pyruvate.
* **Step 3: Sulfite oxidation:** Sulfite is further oxidized to sulfate by the enzyme sulfite oxidase. This reaction also requires molecular oxygen and generates hydrogen peroxide.

**Overall, the catabolism of L-cysteine results in the production of various metabolic intermediates, including α-ketobutyrate, homocysteine, methionine, pyruvate, and sulfate. These products play essential roles in various cellular processes:**

* **Sulfur metabolism:** Cysteine catabolism provides sulfur for the biosynthesis of essential sulfur-containing molecules, such as glutathione, coenzyme A, and various proteins.
* **Amino acid metabolism:** L-cysteine catabolism is interconnected with the metabolism of other amino acids, including methionine, homocysteine, and serine.
* **Redox balance:** The catabolism of L-cysteine generates reducing equivalents, which contribute to maintaining redox homeostasis in the cell.
* **Detoxification:** The transsulfuration pathway is involved in the detoxification of various xenobiotics and reactive oxygen species.
* **H2S production:** The transsulfuration pathway produces hydrogen sulfide (H2S), a signaling molecule with diverse physiological effects.

L-cysteine catabolism is a highly regulated process that is influenced by various factors, including dietary intake, hormonal signals, and cellular stress. Dysregulation of this pathway can lead to various metabolic disorders and disease states.
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Proteins (1)

Compounds (8)