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CENTRAL CARBON → ASPARTATE FAMILY → INDIVIDUAL PATHWAY

Threonine biosynthesis

Follow the carbon skeleton from L-Aspartate to L-Threonine.

What it needs

Aspartate, ATP and reducing power.

What it supplies

L-Threonine. This product can enter downstream cellular reactions; its synthesis depends on the precursor and helper supplies shown.

The pathway

Read from top to bottom. Select an enzyme box to jump to its reaction. Cosubstrates and selected coproducts appear in the account below.

Threonine biosynthesisL-Aspartate to L-Aspartyl-4-phosphate via Aspartate kinase; L-Aspartyl-4-phosphate to L-Aspartate-4-semialdehyde via Aspartate-semialdehyde dehydrogenase; L-Aspartate-4-semialdehyde to L-Homoserine via Homoserine dehydrogenase; L-Homoserine to O-Phospho-L-homoserine via Homoserine kinase; O-Phospho-L-homoserine to L-Threonine via Threonine synthaseL-Aspartate1. Aspartate kinaseATP → ADPRead reaction 1L-Aspartyl-4-phosphate2. Aspartate-semialdehyde dehydrogenaseNADPH → NADP⁺Read reaction 2L-Aspartate-4-semialdehyde3. Homoserine dehydrogenaseReducing power is consumedRead reaction 3L-Homoserine4. Homoserine kinaseATP → ADPRead reaction 4O-Phospho-L-homoserine5. Threonine synthasePLP-dependent; phosphate releasedRead reaction 5L-Threonine

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Reactions and enzymes

1 · Aspartate kinase

L-Aspartate → L-Aspartyl-4-phosphate

Aspartate kinase · EC 2.7.2.4

Inputs, helpers or coproducts: ATP → ADP

2 · Aspartate-semialdehyde dehydrogenase

L-Aspartyl-4-phosphate → L-Aspartate-4-semialdehyde

Aspartate-semialdehyde dehydrogenase · EC 1.2.1.11

Inputs, helpers or coproducts: NADPH → NADP⁺

3 · Homoserine dehydrogenase

L-Aspartate-4-semialdehyde → L-Homoserine

Homoserine dehydrogenase · EC 1.1.1.3

Inputs, helpers or coproducts: Reducing power is consumed

4 · Homoserine kinase

L-Homoserine → O-Phospho-L-homoserine

Homoserine kinase · EC 2.7.1.39

Inputs, helpers or coproducts: ATP → ADP

5 · Threonine synthase

O-Phospho-L-homoserine → L-Threonine

Threonine synthase · EC 4.2.3.1

Inputs, helpers or coproducts: PLP-dependent; phosphate released

Connected pathways

Aspartate from oxaloacetateMethionine biosynthesisLysine biosynthesisIsoleucine biosynthesis

Evidence and scope

This phosphorylated-homoserine route shares upstream intermediates with other aspartate-family branches. This page explains selected documented biochemical reactions. It does not establish that every displayed enzyme occurs in Aquifex, that the pathway is universally essential, or that the book image records a complete organism. Gene symbols name common enzyme activities; organism-specific protein records require separate matching.

Original explanatory diagram and reaction account, based on the records below. Arrows show the biosynthetic reading direction; they do not claim that every reaction is irreversible. Selected protons, water and cofactors are omitted from the overview and are not implied absent.

Compare the related Aquifex annotation group →