Omega-6/3-Quotient: the pathway in the body

Omega-6/3-Quotient is part of the pathway “Omega-6 fatty acids and eicosanoids”. This page shows the whole pathway; the station of Omega-6/3-Quotient is highlighted.

Where this laboratory value sits: EPA — omega-3 fatty acid. EPA is built into the same membranes as arachidonic acid and processed by the same enzymes. The ratio of the two in the membrane determines which molecule is converted more often. Source 6

In brief

Omega-6 fatty acids such as linoleic acid and arachidonic acid are polyunsaturated fatty acids and building blocks of cell membranes. From released arachidonic acid, cells form eicosanoids, short-lived messengers such as prostaglandins and leukotrienes.

The pathway step by step

1. Linoleic acid → γ-Linolenic acid FADS2 (Δ6-desaturase) · NADH, Oxygen Delta-6 desaturase inserts a further double bond into the chain. The same enzyme also processes omega-3 fatty acids, so the two families compete for it. Source 1
2. γ-Linolenic acid → Dihomo-γ-linolenic acid ELOVL5 (elongase) An elongase adds two carbon atoms to the chain, forming dihomo-γ-linolenic acid. Source 1
3. Dihomo-γ-linolenic acid → Arachidonic acid FADS1 (Δ5-desaturase) · NADH, Oxygen Delta-5 desaturase inserts the fourth double bond, forming arachidonic acid. It also comes directly from animal foods. Source 1
4. Arachidonic acid → In the cell membrane Arachidonic acid is built into the phospholipids of cell membranes. Most of it stays there until a stimulus reaches the cell. Source 2
5. Free arachidonic acid → PGH₂ COX-1, COX-2 · Oxygen, Haem The cyclooxygenases COX-1 and COX-2 add oxygen and form a ring. PGH₂ is formed via the intermediate PGG₂. Source 3
6. Free arachidonic acid → LTA₄ 5-Lipoxygenase · FLAP, Calcium 5-lipoxygenase moves with calcium to the nuclear membrane and works there with the helper protein FLAP. LTA₄ is formed via the intermediate 5-HPETE. Source 4
7. PGH₂ → Prostaglandins Synthases Tissue-specific synthases turn PGH₂ into various prostaglandins. They break down quickly and therefore act only close to where they are made. Source 3
8. PGH₂ → Thromboxane A₂ Thromboxane synthase In platelets, thromboxane synthase converts PGH₂ into thromboxane A₂. It makes platelets stick together and vascular muscle contract. Source 3
9. LTA₄ → LTB₄ LTA₄ hydrolase LTA₄ hydrolase turns LTA₄ into leukotriene B₄. It acts as an attractant for white blood cells. Source 5
10. LTA₄ → Cysteinyl leukotrienes LTC₄ synthase · Glutathione LTC₄ synthase attaches glutathione to LTA₄. This gives rise in turn to LTC₄, LTD₄ and LTE₄, which act on smooth muscle and blood vessels. Source 4, 5
11. EPA → Eicosanoids from EPA COX, lipoxygenases When COX and lipoxygenases convert EPA, series-3 prostaglandins and series-5 leukotrienes are formed. They bind to the same receptors but act more weakly there. Source 6

Cofactors in this pathway

• Iron — Haem iron in the cyclooxygenases COX-1 and COX-2; non-haem iron in 5-lipoxygenase Source 3, 4In the ORY catalogue as a laboratory value: Eisen
• Calcium — Guides cPLA2 and 5-lipoxygenase to the membranes where arachidonic acid is released Source 2, 4In the ORY catalogue as a laboratory value: Calcium (intrazellulär)
• Glutathione — Attached to LTA₄ by LTC₄ synthase, forming the cysteinyl leukotrienes Source 4, 5In the ORY catalogue as a laboratory value: Glutathion (GSH)
• NADH — Electron donor for the desaturases FADS1 and FADS2, which insert double bonds Source 1

Sources

1. Brenna JT, Kothapalli KSD. New understandings of the pathway of long-chain polyunsaturated fatty acid biosynthesis. Curr Opin Clin Nutr Metab Care 2022 · PubMed 34937850
2. Leslie CC. Regulation of the specific release of arachidonic acid by cytosolic phospholipase A2. Prostaglandins Leukot Essent Fatty Acids 2004 · PubMed 15041029
3. Smith WL, DeWitt DL, Garavito RM. Cyclooxygenases: structural, cellular, and molecular biology. Annu Rev Biochem 2000 · PubMed 10966456
4. Peters-Golden M, Brock TG. 5-lipoxygenase and FLAP. Prostaglandins Leukot Essent Fatty Acids 2003 · PubMed 12895592
5. Wan M, Tang X, Stsiapanava A et al. Biosynthesis of leukotriene B4. Semin Immunol 2017 · PubMed 29042025
6. Calder PC. Marine omega-3 fatty acids and inflammatory processes: Effects, mechanisms and clinical relevance. Biochim Biophys Acta 2015 · PubMed 25149823

Whole pathway: Omega-6 fatty acids and eicosanoids

Related pathways

• Omega-3 fatty acids — epa
• Nitrosative stress — Eisen, Calcium (intrazellulär)
• 8-OHdG — Eisen, Glutathion (GSH)
• Calprotectin — Eisen, Calcium (intrazellulär)
• Copper — Eisen, Glutathion (GSH)

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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