A cytochrome P450 monooxygenase that primarily catalyzes the epoxidation of 11,12 double bond of (5Z,8Z,11Z,14Z)-eicosatetraenoic acid (arachidonate) forming 11,12-epoxyeicosatrienoic acid (11,12-EET) regioisomer. Mechanistically, uses molecular oxygen inserting one oxygen atom into a substrate, and reducing the second into a water molecule, with two electrons provided by NADPH via cytochrome P450 reductase (CPR; NADPH--hemoprotein reductase). an organic molecule + O2 + reduced [NADPH--hemoprotein reductase] = an alcohol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] (5Z,8Z,11Z,14Z)-eicosatetraenoate + O2 + reduced [NADPH--hemoprotein reductase] = 11,12-epoxy-(5Z,8Z,14Z)-eicosatrienoate + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Lipid metabolism; arachidonate metabolism. Liver, brain, kidney, and intestine, with trace amounts in lung and heart. Belongs to the cytochrome P450 family.