CENTRAL CARBON → BRANCHED-CHAIN AMINO ACIDS → INDIVIDUAL PATHWAY

Isoleucine biosynthesis

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

What it needs

A source of 2-oxobutanoate, pyruvate, reducing power and nitrogen.

What it supplies

L-Isoleucine. 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.

Open full-resolution vector diagram ↗

Reactions and enzymes

1 · Threonine deaminase (IlvA)

L-Threonine → 2-Oxobutanoate

Threonine deaminase (IlvA) · EC 4.3.1.19

Inputs, helpers or coproducts: Ammonia released

This is a representative threonine-dependent entry, not an assignment to Aquifex.

2 · Acetohydroxyacid synthase

2-Oxobutanoate + pyruvate → 2-Aceto-2-hydroxybutanoate

Acetohydroxyacid synthase · EC 2.2.1.6

Inputs, helpers or coproducts: CO₂ released

3 · Ketol-acid reductoisomerase (IlvC)

2-Aceto-2-hydroxybutanoate → 2,3-Dihydroxy-3-methylpentanoate

Ketol-acid reductoisomerase (IlvC) · EC 1.1.1.86

Inputs, helpers or coproducts: NADPH → NADP⁺

4 · Dihydroxy-acid dehydratase (IlvD)

2,3-Dihydroxy-3-methylpentanoate → 3-Methyl-2-oxopentanoate

Dihydroxy-acid dehydratase (IlvD) · EC 4.2.1.9

5 · Branched-chain amino-acid aminotransferase (IlvE)

3-Methyl-2-oxopentanoate → L-Isoleucine

Branched-chain amino-acid aminotransferase (IlvE) · EC 2.6.1.42

Inputs, helpers or coproducts: Glutamate supplies the amino group

Connected pathways

Threonine biosynthesis Valine biosynthesis Leucine biosynthesis

Evidence and scope

Aquifex is discussed with a citramalate alternative: pyruvate + acetyl-CoA → citramalate → citraconate → 3-methylmalate → 2-oxobutanoate. See KEGG M00535; the downstream branched-chain steps then follow. 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.