Food Chemistry and Fish in Nutrition

4.2.3. Oxidation of a fatty acid with an odd number of carbon atoms

Fatty acids with an odd number of carbon atoms are oxidized by the pathway of β - oxidation, producing acetyl-CoA until a three- carbon (propionyl-CoA) residue remains. This compound is then converted to succinyl-CoA, a constituent of the citric acid cycle and metabolized.

Propionyl-CoA carboxylase

Propionyl CoA + CO₂ + H₂O → D-methylmalonyl-CoA

D-Methylmalonyl-CoA is converted to its steroisomer, L- methylmalonyl-CoA, by methylmalonyl-coA racemase before its final isomerization to succinyl-CoA by the enzyme methylmalonyl-CoA isomerase.

Methylmalonyl-CoA racemase

D-Methylmalonyl-CoA ↔ L- methylmalonyl-CoA

Methylmalonyl-CoA isomerase

L- methylmalonyl-CoA ↔ Succinyl-CoA

Thus the propionyl residue from an odd-chain fatty acid is the only part of a fatty acid that is glucogenic.