Eicosatetraenoic acid
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Eicosatetraenoic acid (ETA) designates any straight chain tetra-unsaturated 20-carbon fatty acid. The pure compounds, which are rarely encountered, are colorless oils. Two isomers, both of them essential fatty acids, are of particular interest:
- all-cis-5,8,11,14-eicosatetraenoic acid is an ω-6 fatty acid with the trivial name arachidonic acid. It is formed by a desaturation of dihomo-gamma-linolenic acid (DGLA, 20:3 ω-6).
- all-cis-8,11,14,17-eicosatetraenoic acid is an ω-3 fatty acid. It is an intermediate between stearidonic acid (18:4 ω-3) and eicosapentaenoic acid (EPA, 20:5 ω-3)
Some chemistry sources define 'arachadonic acid' to designate any of the eicosatetraenoic acids. However, almost all writings in biology, medicine, and nutrition limit the use of the term 'arachidonic acid' to all-cis-5,8,11,14-eicosatetraenoic acid (ω-6).