Metabolic pathway
Branched-chain amino acids
Breaks down leucine, which because of its branching does not fit the usual pathways. It ends in HMG-CoA, so its carbon ends up in ketone bodies and in acetyl-CoA, never in glucose.
- In
- Leucine + α-Ketoglutarate + Coenzyme A + NAD⁺ + FAD + ATP + 2 Water
- Out
- Glutamate + NADH + Proton + FADH₂ + ADP + Inorganic phosphate + Acetoacetate + Acetyl-CoA
- Location
- Mitochondrial matrix
Fun facts
- Branched-chain amino acid aminotransferaseThis first enzyme is abundant above all in muscle, not in the liver. That is why the branched-chain amino acids are the only ones muscle breaks down on its own, without sending them to the liver first.
- Branched-chain α-keto acid dehydrogenaseWhen this complex fails, the α-keto acids build up and show up in the urine with a characteristic smell. Hence the name of the disease: maple syrup urine disease.
Reactions
| # | Enzyme | ΔG°′ |
|---|---|---|
| 1 | Branched-chain amino acid aminotransferaseEC 2.6.1.42Leucine + α-Ketoglutarate ⇌ α-Ketoisocaproate + Glutamate | — |
| 2 | Branched-chain α-keto acid dehydrogenaseEC 1.2.4.4 · irreversibleα-Ketoisocaproate + Coenzyme A + NAD⁺ → Isovaleryl-CoA + Carbon dioxide + NADH + Proton | — |
| 3 | Isovaleryl-CoA dehydrogenaseEC 1.3.8.4 · irreversibleIsovaleryl-CoA + FAD → 3-Methylcrotonyl-CoA + FADH₂ | — |
| 4 | 3-methylcrotonyl-CoA carboxylaseEC 6.4.1.4 · irreversible3-Methylcrotonyl-CoA + Carbon dioxide + ATP + Water → 3-Methylglutaconyl-CoA + ADP + Inorganic phosphate | — |
| 5 | 3-methylglutaconyl-CoA hydrataseEC 4.2.1.183-Methylglutaconyl-CoA + Water ⇌ HMG-CoA | — |
| 6 | HMG-CoA lyaseEC 4.1.3.4 · irreversibleHMG-CoA → Acetoacetate + Acetyl-CoA | — |
0 of 6 reactions with a documented ΔG.
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The data sheet includes the map. The logo goes at the bottom.
Sources
- Nelson, D. L. & Cox, M. M. (2021). Lehninger. Principios de bioquímica, 8.ª ed., ch. 18