Binding Site

Nitrite/sulphite reductase iron-sulphur/sirohaem-binding site (IPR006066)

Short name: NO2/SO3_Rdtase_FeS/sirohaem_BS


Nitrite reductases and bacterial sulphite reductases catalyse the 6-electron reduction of nitrite (sulphite) to ammonia (sulphide) [PMID: 2204158]. On the basis of physiological function, 2 types of nitrite reductase can be defined: the assimilatory type, which is involved in nitrate assimilation (denitrification); and the dissimilatory type, which is responsible for nitrate respiration function. Assimilatory nitrite reductases contain a prosthetic group termed sirohaem (an iron tetra-hydroporphyrin of the isobacteriochlorin type, with 8 carboxylic acid-containing peripheral sidechains), and an iron-sulphur cluster. Similarly, there are 2 types of sulphite reductase: the assimilatory type, which participate in the synthesis of sulphur-containing compounds; and the dissimilatory type, which are terminal reductases in the reduction of sulphate. Assimilatory sulphite reductases can catalyse 6-electron reduction without the formation of free intermediates, while dissimilatory reductases can produce trithionate and thiosulphate in addition to sulphide. Both types of reductase contain sirohaem and iron-sulphur clusters. A region of sequence similarity, about 80 amino acids long, is shared by assimilatory nitrite [PMID: 2204158] and sulphite reductases [PMID: 1704886, PMID: 2670946]. Four conserved Cys residues are suggested to be involved in binding the sirohaem group and/or the iron-sulphur centre [PMID: 2670946].

GO terms

Biological Process

GO:0055114 oxidation-reduction process

Molecular Function

GO:0020037 heme binding
GO:0051536 iron-sulfur cluster binding
GO:0016491 oxidoreductase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE patterns