PMID:9352929

Citation	Cramm, R, Siddiqui, RA and Friedrich, B (1997) Two isofunctional nitric oxide reductases in Alcaligenes eutrophus H16. J. Bacteriol. 179:6769-77
Abstract	Two genes, norB and norZ, encoding two independent nitric oxide reductases have been identified in Alcaligenes eutrophus H16. norB and norZ predict polypeptides of 84.5 kDa with amino acid sequence identity of 90%. While norB resides on the megaplasmid pHG1, the norZ gene is located on a chromosomal DNA fragment. Amino acid sequence analysis suggests that norB and norZ encode integral membrane proteins composed of 14 membrane-spanning helices. The region encompassing helices 3 to 14 shows similarity to the NorB subunit of common bacterial nitric oxide reductases, including the positions of six strictly conserved histidine residues. Unlike the Nor enzymes characterized so far from denitrifying bacteria, NorB and NorZ of A. eutrophus contain an amino-terminal extension which may form two additional helices connected by a hydrophilic loop of 203 amino acids. The presence of a NorB/NorZ-like protein was predicted from the genome sequence of the cyanobacterium Synechocystis sp. strain PCC6803. While the common NorB of denitrifying bacteria is associated with a second cytochrome c subunit, encoded by the neighboring gene norC, the nor loci of A. eutrophus and Synechocystis lack adjacent norC homologs. The physiological roles of norB and norZ in A. eutrophus were investigated with mutants disrupted in the two genes. Mutants bearing single-site deletions in norB or norZ were affected neither in aerobic nor in anaerobic growth with nitrate or nitrite as the terminal electron acceptor. Inactivation of both norB and norZ was lethal to the cells under anaerobic growth conditions. Anaerobic growth was restored in the double mutant by introducing either norB or norZ on a broad-host-range plasmid. These results show that the norB and norZ gene products are isofunctional and instrumental in denitrification.
Links	PubMed PMC179608
Keywords	Alcaligenes/enzymology; Alcaligenes/genetics; Amino Acid Sequence; Base Sequence; Cloning, Molecular; Genes, Bacterial; Isoenzymes/genetics; Isoenzymes/metabolism; Membrane Proteins/genetics; Models, Molecular; Molecular Sequence Data; Nitric Oxide/metabolism; Oxidoreductases/genetics; Oxidoreductases/metabolism; Plasmids/genetics; Protein Conformation; Restriction Mapping; Sequence Analysis, DNA; Sequence Homology, Amino Acid
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
CUPNE:A1JHG0		GO:0016966: nitric oxide reductase activity	ECO:0000316:	UniProtKB:Q46R31	F		FIGURE 5 demonstrates that in the absence of norB (and norZ) the organism cannot preform anaerobic nitrification.	complete CACAO 2231
CUPNE:A1JHG0	enables	GO:0016966: nitric oxide reductase activity	ECO:0000316: genetic interaction evidence used in manual assertion	UniProtKB:Q46R31	F		Seeded From UniProt	complete

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