Arachidonic acid

Overview
Arachidonic acid (AA) is an omega-6 fatty acid 20:4(ω-6). It is the counterpart to the saturated arachidic acid found in peanut oil, (L. arachis – peanut.)

Chemical characteristics
Chemically, arachidonic acid is a carboxylic acid with a 20-carbon chain and four cis double bonds; the first double bond is located at the sixth carbon from the omega end.

Some chemistry sources define 'arachidonic acid' to designate any of the eicosatetraenoic acids. However, almost all writings in biology, medicine and nutrition limit the term to all-cis 5,8,11,14-eicosatetraenoic acid.

Biological role
Arachidonic acid is a polyunsaturated fatty acid that is present in the phospholipids (especially phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositides) of membranes of the body's cells, and is abundant in the brain.

It is also involved in cellular signaling as a second messenger.

It is the source of several other molecules with specific roles, as described in the next section.

Synthesis and cascade
Arachidonic acid is freed from phospholipid molecule by the enzyme phospholipase A2, which cleaves off the fatty acid precursor (usually linoleic acid).

Arachidonic acid is a precursor in the production of eicosanoids:
 * the enzymes cyclooxygenase and peroxidase lead to Prostaglandin H2, which in turn is used to produce the prostaglandins, prostacyclin, and thromboxanes.
 * the enzyme 5-lipoxygenase leads to 5-HPETE, which in turn is used to produce the leukotrienes.
 * arachidonic acid is also used in the biosynthesis of anandamide.

The production of these derivatives, and their action in the body, are collectively known as the arachidonic acid cascade; see essential fatty acid interactions for more details.

Arachidonic acid as an essential fatty acid
Arachidonic acid is one of the essential fatty acids required by most mammals. Some mammals lack the ability to&mdash;or have a very limited capacity to&mdash;convert linoleic acid into arachidonic acid, making it an essential part of their diet. Since little or no arachidonic acid is found in plants, such animals are obligate carnivores; the cat is a common example.
 * For a more detailed discussion of the term 'essential', see Essential fatty acid – What is &quot;essential&quot;?