Cytochrome P450 nitric oxide reductase (P450nor) is involved in a dissimilatory reduction of nitrite. Acts as a nitric oxide reductase. Is able to reduce nitrate and nitrite to a gaseous form of N2O when oxygen supply is limited or discontinued. May function as a detoxification mechanism.
This protein is found in denitrifying organisms such as Fusarium oxysporum. It is a member of the cytochrome P450 superfamily, which are heme-thiolate enzymes. There are two isoforms of P450nor in F. oxysporum, one of which uses NADH as cofactor exclusively, while the other uses NADH or NADPH.
P450nor catalyses the NAD(P)H-dependent reduction of two molecules of the free radical, nitric oxide (NO), to nitrous oxide (N2O). The reaction is unusual because it involves direct electron transfer, in the form of a hydride, from NAD(P)H to a redox protein (heme) that contains only a one-electron redox centre.
P450nor appears to have an important role in protecting the fungus from NO inhibition of mitochondria and other cellular damage that may result from the reaction of NO with other molecules such as oxygen or superoxide to form biologically hazardous compounds.
Defined by 4 residues: THR:A-243SER:A-286CYS:A-352ASP:A-393
