|MadSci Network: Biochemistry|
Alpha-lenolenic acid (ALA) is a structural component of the cell membrane in phospholipids (such as phosphatidylcholine). The action of phospholipase can liberate some of this omega-3 fatty acid. This in turn is converted to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which have been implicated in reducing the risk of cardiovascular disease. As you noted, the overall conversion of free ALA to EPA and DHA is relatively low. In fact, much of the ALA ingested (up to 30% in human males, somewhat lower in females) is converted to energy through the normal beta-oxidation pathway for fatty acids.
Since I am actually a plant scientist, I would be remiss if I failed to note that in plants ALA plays another role. ALA is converted to jamonic acid and methyl-jasmonate. Methyl-jasmonate serves as a signaling molecule in defense and many developmental processes in the plant.
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