 The 12("S")-HpETE formed in tissues, it is suggested, may similar rearrange non-enzymatically to form HxA3 and HXB3.Unlike the products made by ALOX12 and ALOXE3, which are stereospecific in forming only HxA3 and HxB3, however, this non-enzymatic production of hepoxilins may form a variety of hepoxilin isomers and occur as an artifact of tissue processing.Finally, cellular peroxidases readily and rapidly reduce 12("S")-HpETE to its hydroxyl analog, 12"S"-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12"S"-HETE; see 12-hydroxyeicosatetraenoic acid; this reaction competes with the hepoxilin-forming reaction and in cells expressing very high peroxidase activity may be responsible for blocking the formation of the hepoxilins.