Food Chemistry and Fish in Nutrition

4.2.4. Oxidation of unsaturted fatty acids

Oxidation of unsaturated fatty acids occurs by a modified beta- oxidation pathway.

1. Initial reaction 

 

The CoA ester of these acids are degraded by the enzymes normally responsible for β - oxidation until either a Δ³-cis- acyl-CoA compound or Δ⁴-Cis-acyl-CoA compound is formed, depending upon the position of the double bonds.

2. Reaction of Isomerase

The former compound is isomerized (Δ³ cis-Δ² 1 CoA isomerase) to the corresponding D² -trans-CoA stage of β - oxidation for subsequent hydration and oxidation.

3. One cycle of Beta Oxidation

Any Δ⁴ -cis-acy1-CoA either remaining, as in the case of linoleic acid, it is converted to Δ² -trans enoy1-CoA by an NADP dependent enzyme, Δ² - trans - Δ³-cis dienoy1-CoA reductase.

4. Action of Acyl-CoA dehydrogenase

Δ-cis (or trans) Δ² enoy1-CoA isomerase will attack the trans double bond to produce Δ² - trans enoy1-CoA, an intermediate in beta oxidation.

This compound is further metobolised via β - oxidation

5.  Action of  2, 4-Dienoyl-CoA reductase

Action of Enoyl-CoA Isomerase

Enoyl Co A isomerase then coverts Δ³ isomer to Δ² isomer

∆3-cis (or trans)   ∆2 - trans enoy1-CoA isomerase will attack the trans  double bond to produce ∆2- trans enoy1-CoA, an intermediate in β- oxidation.

This compound is further metabolized via β-oxidation.