The effect of nitrite on cytochrome oxidase

Nitrite inhibits the oxygen uptake by the system ferrocytochrome c-cytochrome oxidase with Ki = 1.5 mM. In the absence of ferrocytochrome c the oxygen uptake by cytochrome oxidase in the presence of nitrite was observed indicating that the enzyme has some nitrite oxidase activity. Nitrite induces changes in optical difference spectra of cytochrome oxidase and, in particular, the formation of the transient band at 607 nm. The reciprocal relation was observed between the intensity of this band and the rate of the oxygen uptake by cytochrome oxidase. This means that the form of the enzyme with this band does not involved in the nitrite oxidase activity. It is suggested that the nitrite oxidase activity relates to the oxygen binding site rather than the cytochrome c binding site of the enzyme.