Nitrite-Nitric oxide cycle

In normoxia, NOS is functional and generates NO, which is oxidized by Hb and Mb to nitrate, and by CcOx and Cp to nitrite. Nitrite is also derived from the diet as well as the normoxic oxidation of nitrite by CYP450 enzymes. In hypoxia, nitrate is reduced to nitrite by anaerobic commensal bacteria and nitrite is reduced to bioactive NO by a number of mammalian nitrite reductase enzymes, including Hb, Mb, Ngb, xanthine oxidoreductase, aldehyde oxidase, sulfite oxidase, components of the mitochondrial electron transport chain, and NOS.