Fig. 1.
Consecutive oxygenation of arachidonic acid by 5-LOX and COX-2 gives a diendoperoxide as the major and 5,11- and 5,15-diHETE as by-products. Further enzymatic or non-enzymatic transformation of the di-endoperoxide gives HKD2 and HKE2. The diendoperoxide can be cleaved by FeCl2 or hematin into three aldehydes. COX-2 reacts 5S-HETE with 3 molecules of oxygen, and their incorporation into the di-endoperoxide and subsequent fate in the HKs and other products is marked by the different colors.