Mitochondrial matrix
β-Oxidation
Four steps, repeated. Two carbons off per round.
Per round: 1 FADH₂ · 1 NADH · 1 acetyl-CoA
This mnemonic, unpacked word by word →
The same chemistry as the back half of the TCA cycle: oxidize with FAD, hydrate, oxidize with NAD, then cleave.
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Fatty acyl-CoA (cytosol)
Fatty acyl-CoA (matrix)
Carnitine acyltransferase Irate-limiting
“(entry)” → Carnitine acyltransferase I
Rate-limiting. Inhibited by malonyl-CoA, the first committed intermediate of fatty acid synthesis.
1
Acyl-CoA
Enoyl-CoA
Acyl-CoA dehydrogenase FADH₂
“Oxidize” → Acyl-CoA dehydrogenase
Medium-chain form (MCAD) deficiency causes hypoketotic hypoglycemia.
2
Enoyl-CoA
3-Hydroxyacyl-CoA
Enoyl-CoA hydratase adds H₂O
“Hydrate” → Enoyl-CoA hydratase
3
3-Hydroxyacyl-CoA
3-Ketoacyl-CoA
3-Hydroxyacyl-CoA dehydrogenase NADH
“Oxidize” → 3-Hydroxyacyl-CoA dehydrogenase
4
3-Ketoacyl-CoA
Acetyl-CoA + shortened acyl-CoA
Thiolase
“Thiolyze” → Thiolase
Releases acetyl-CoA and hands back a chain two carbons shorter to repeat the cycle.