Arachidonic acid
EETS are epoxide eicosatrienoic acid metabolites of arachidonic acid (a straight chain Eicosatetraenoic acid, omega-6 fatty acid). Arachidonic acid has 4 cis double bonds (see Cis–trans isomerism which are abbreviated with the notation "Z" in the IUPAC Chemical nomenclature used here. These double bonds are located between carbons 5-6, 8-9, 11-12, and 14-15; arachidonic acid is therefore 5"Z",8"Z",11"Z",14"Z"-eicosatetraenoic acid. Cytochrome P450 epoxygenases attack these double bonds to form their respective eicosatrienoic acid epoxide regioisomers (see Structural isomer, section on position isomerism (regioisomerism)) viz., 5,6-EET (i.e. 5,6-epoxy-8"Z",11"Z",14"Z"-eicosatrienoic acid), 8,9-EET (i.e. 8,9-epoxy-5"Z",11"Z",14"Z"-eicosatrienoic acid), 11,12-EET (i.e. 11,12-epoxy-5"Z",8"Z",14"Z"-eicosatrienoic acid), or, as drawn in the attached figure, 14,15-EET (i.e. 14,15-epoxy-5"Z",8"Z",11"Z"-eicosatrienoic acid). The enzymes generally form both "R"/"S" enantiomers at each former double bond position; for example, cytochrome P450 epoxidases metabolize arachidonic acid to a mixture of 14"R",15"S"-EET and 14"S",15"R"-EET.