title: Molecular and catalytic properties of a novel cytochrome c nitrite reductase from nitrate-reducing haloalkaliphilic sulfur-oxidizing bacterium Thioalkalivibrio nitratireducens.
abstract: A highly active cytochrome c nitrite reductase from the haloalkaliphilic sulfur-oxidizing non-ammonifying bacterium Tv. nitratireducens strain ALEN 2 (TvNiR) was isolated and purified to apparent electrophoretic homogeneity. The enzyme catalyzes reductive conversion of nitrite and hydroxylamine to ammonia without release of any intermediates, as well as reduction of sulfite to sulfide. TvNiR also possesses peroxidase activity. In solution TvNiR exists as a stable hexamer with molecular mass of about 360kDa. Each TvNiR subunit with molecular mass of 64kDa contains, as defined from spectral properties and sequence analysis, eight c-type haems. Seven of them are coordinated by the characteristic CXXCH motifs for haem c binding, while one is bonded by the unique CXXCK motif. So far, this motif coordinating the catalytic haem was found only in bacterial cytochrome c nitrite reductases (ccNiRs). All the residues essential for catalysis in the known ccNiRs were also identified in TvNiR. However, TvNiR is only distantly related to known bacterial ammonifying dissimilatory ccNiRs, sharing no more than 20% homology.
authors.affiliation: Bach Institute of Biochemistry, Leninsky pr. 33, 119071 Moscow, Russia. ttikhonova@inbi.ras.ru
authors.forename: Tamara V
authors.initials: TV
authors.lastname: Tikhonova
authors.forename: Alvira
authors.initials: A
authors.lastname: Slutsky
authors.forename: Alexey N
authors.initials: AN
authors.lastname: Antipov
authors.forename: Konstantin M
authors.initials: KM
authors.lastname: Boyko
authors.forename: Konstantin M
authors.initials: KM
authors.lastname: Polyakov
authors.forename: Dimitry Y
authors.initials: DY
authors.lastname: Sorokin
authors.forename: Renata A
authors.initials: RA
authors.lastname: Zvyagilskaya
authors.forename: Vladimir O
authors.initials: VO
authors.lastname: Popov
mesh_terms: D000595:Amino Acid Sequence; D045263:Cytochromes a1 / Q000737:chemistry* / Q000378:metabolism*; D003575:Cytochromes c1 / Q000737:chemistry* / Q000378:metabolism*; D042001:Ectothiorhodospiraceae / Q000201:enzymology; D006418:Heme / Q000032:analysis; D007700:Kinetics; D008969:Molecular Sequence Data; D009565:Nitrate Reductases / Q000737:chemistry* / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D016415:Sequence Alignment; D013053:Spectrophotometry
chemical_list: D006418:Heme; D045263:Cytochromes a1; D003575:Cytochromes c1; D009565:Nitrate Reductases; C054690:nitrate reductase (cytochrome)