methionine biosynthetic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways resulting in the formation of methionine (2-amino-4-(methylthio)butanoic acid), a sulfur-containing, essential amino acid found in peptide linkage in proteins. [GOC:jl, ISBN:0198506732]

Methionine biosynthesis is a complex process that involves the conversion of aspartate to methionine, a critical amino acid with essential roles in protein synthesis, methylation reactions, and the synthesis of other important molecules. The process is tightly regulated and consists of several steps, each catalyzed by specific enzymes.

**1. Aspartate to Homoserine:**

- The initial step involves the conversion of aspartate to homoserine.
- This reaction is catalyzed by aspartokinase, which phosphorylates aspartate to form aspartyl phosphate.
- Aspartyl phosphate is then reduced to homoserine by aspartate semialdehyde dehydrogenase.

**2. Homoserine to Threonine:**

- Homoserine is converted to threonine via the action of homoserine dehydrogenase.
- This step involves the oxidation of homoserine to α-ketobutyrate and the subsequent reduction of α-ketobutyrate to threonine.

**3. Threonine to O-phosphohomoserine:**

- Threonine is phosphorylated to form O-phosphohomoserine by threonine kinase.
- This phosphorylation is crucial for the next step in the pathway.

**4. O-phosphohomoserine to Cystathionine:**

- O-phosphohomoserine reacts with cysteine to form cystathionine in a reaction catalyzed by cystathionine β-synthase.
- This step marks the entry of sulfur into the pathway.

**5. Cystathionine to Homocysteine:**

- Cystathionine is cleaved by cystathionine γ-lyase to produce homocysteine and α-ketobutyrate.
- This reaction is reversible and is regulated by the availability of both substrates.

**6. Homocysteine to Methionine:**

- Homocysteine is methylated to methionine by tetrahydrofolate reductase (THF reductase).
- This step requires N5-methyltetrahydrofolate as a methyl donor.
- The reaction is catalyzed by tetrahydrofolate reductase (THF reductase) and is the final step in methionine biosynthesis.'
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Proteins (5)

Compounds (5)