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d 1 haem biogenesis – assessing the roles of three nir gene products
Author(s) -
Zajicek Richard S.,
Bali Shilpa,
Arnold Simon,
Brindley A. Amanda,
Warren J. Martin,
Ferguson Stuart J.
Publication year - 2009
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2009.07354.x
Subject(s) - biochemistry , nitrite reductase , cytochrome , chemistry , heme , cytochrome b , operon , cytochrome c , paracoccus denitrificans , cytochrome p450 reductase , coenzyme q – cytochrome c reductase , enzyme , biology , gene , mitochondrion , escherichia coli , mitochondrial dna , nitrate reductase
The synthesis of the modified tetrapyrrole known as d 1 haem requires several dedicated proteins which are coded for by a set of genes that are often found adjacent to the structural gene, nirS , for cytochrome cd 1 nitrite reductase. NirE, the product of the first gene in the nir biogenesis operon, was anticipated to catalyse the conversion of uroporphyrinogen III into precorrin‐2; this was confirmed, but it was shown that this enzyme is less sensitive to product inhibition than similar enzymes that function in other biosynthetic pathways. Sequence analysis suggesting that one of these proteins, NirN, is a c ‐type cytochrome, and has similarity to the part of cytochrome cd 1 that binds d 1 , was validated by recombinant production and characterization of NirN. A NirN– d 1 haem complex was demonstrated to release the cofactor to a semi‐apo form of cytochrome cd 1 from which d 1 was extracted, suggesting a role for NirN in the assembly of cytochrome cd 1 (NirS). However, inactivation of nirN surprisingly led to only a marginal attenuation of growth of Paracoccus pantotrophus under anaerobic denitrifying conditions. As predicted, NirC is a c ‐type cytochrome; it was shown in vitro to be an electron donor to the NirN– d 1 complex.