Essential fatty acids (EFAs) are metabolized to longer, more unsaturated fatty acids via a series of enzymatic reactions involving desaturases and elongases. Specifically, linoleic acid (LA) and alpha-linolenic acid (ALA) are converted into other important fatty acids.
Here's a breakdown of the metabolic pathways:
1. Overview of EFA Metabolism
The metabolism of EFAs involves a series of enzyme-catalyzed reactions. These reactions consist of:
- Desaturation: Adding a double bond to the fatty acid chain.
- Elongation: Lengthening the fatty acid chain by adding two carbon atoms.
2. Linoleic Acid (LA) Metabolism (Omega-6 Pathway)
Linoleic acid (18:2 n-6), an omega-6 fatty acid, is metabolized as follows:
- Step 1: Desaturation. LA is desaturated by Δ6-desaturase (also known as FADS2) to form gamma-linolenic acid (GLA) (18:3 n-6).
- Step 2: Elongation. GLA is then elongated by elongase to form dihomo-gamma-linolenic acid (DGLA) (20:3 n-6).
- Step 3: Desaturation. DGLA is further desaturated by Δ5-desaturase (also known as FADS1) to form arachidonic acid (AA) (20:4 n-6).
3. Alpha-Linolenic Acid (ALA) Metabolism (Omega-3 Pathway)
Alpha-linolenic acid (18:3 n-3), an omega-3 fatty acid, is metabolized as follows:
- Step 1: Desaturation. ALA is desaturated by Δ6-desaturase to form stearidonic acid (18:4 n-3).
- Step 2: Elongation. Stearidonic acid is elongated to eicosatetraenoic acid (20:4 n-3).
- Step 3: Desaturation. Eicosatetraenoic acid is further desaturated by Δ5-desaturase to form eicosapentaenoic acid (EPA) (20:5 n-3).
- Step 4: Elongation and Desaturation. EPA can be further metabolized to docosahexaenoic acid (DHA) (22:6 n-3) through elongation and another desaturation step.
4. Enzyme Competition and Dietary Factors
It is important to note that Δ6-desaturase is a shared enzyme between the omega-6 and omega-3 pathways. Therefore, a high intake of LA can compete with ALA for this enzyme, potentially reducing the conversion of ALA to EPA and DHA. Other factors like age, sex, and certain nutrients (e.g., zinc, iron, vitamin B6) can also influence the activity of these enzymes.
5. Summary
In summary, essential fatty acids are metabolized through desaturation and elongation reactions to form longer-chain polyunsaturated fatty acids. LA is converted to DGLA and AA, while ALA is converted to EPA and DHA. These metabolites play crucial roles in various physiological processes, including inflammation, brain function, and cardiovascular health.
