Cytochrome cd1 (cyt cd1) nitrite reductase is a dimeric enzyme of the bacterial periplasm that plays a key role in denitrification, the respiratory reduction of nitrite to nitric oxide in the nitrogen cycle. Each subunit of the cyt cd1 dimer contains one cytochrome c and one d1 haem group [PMID:12556530]. The active site contains a specialised d1 haem, where the nitrite substrate is bound and reduced. This d1 haem is bound in an 8-bladed beta-propeller, which is also found in some members of the WD40 repeat-containing proteins (IPR001680).
Defined by 6 residues: CYS:A-47CYS:A-50HIS:A-51MET:A-88HIS:A-327HIS:A-369