The reaction is catalysed by two types of enzymes, found in the perimplasm of denitrifying bacteria. One type comprises proteins containing multiple copper centres, the other a heme protein, cytochrome cd1. Acceptors include c-type cytochromes such as cytochrome c-550 or cytochrome c-551 from Paracoccus denitrificans or Pseudomonas aeruginosa, and small blue copper proteins such as azurin and pseudoazurin. Cytochrome cd1 also has oxidase and hydroxylamine reductase activities. May also catalyse the reaction of hydroxylamine reductase (EC 184.108.40.206) since this is a well-known activity of cytochrome cd1.
EC 220.127.116.11 created 1961, modified 1976, modified 2001, modified 2002 (EC 18.104.22.168 created 1961 as EC 22.214.171.124, transferred 1964 to EC 126.96.36.199, modified 1976, incorporated 2002, EC 188.8.131.52 created 1965, incorporated 2002)