Glutathione peroxidase 1 (GPX1) (Bryant et al. 1982, Sutherland et al. 2001), 2 (GPX2) (Chu et al. 1993), and 4 (Bryant et al. 1982, Sutherland et al. 2001) are involved in converting 12S-hydroperoxy-eicosatetraenoic acid (12S-HpETE) to 12S-hydro-eicosatetraenoic acid (12S-HETE). GPXs are selenoenzymes that are responsible for reducing the cellular peroxide. Cellular GPXs compete with hepoxilins A3 (HXA3) synthase for 12S-HpETE as substrate either to produce 12S-HETE or to convert to HXA3, respectively.