Heme/Copper Assembly Mediated Nitrite and Nitric Oxide Interconversion

The hemea3/CuB active site of cytochrome c oxidase is responsible for cellular nitrite reduction to nitric oxide; the same center can return NO to the nitrite pool via oxidative chemistry. Here, we show that a partially reduced heme/Cu assembly reduces NO2– ion, producing nitric oxide. The heme serves as the reductant, but the CuII ion is also required. In turn, a μ-oxo heme-FeIII–O–CuII complex facilitates NO oxidation to nitrite; the final products are the reduced heme and CuII–nitrito complexes.