Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Pivot Concepts:
Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Target Concepts:
Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Query: EC:1.7.1.4 (
nitrite reductase
)
1,847
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
Nitrosocyanin (NC), a soluble, red Cu protein isolated from the ammonia-oxidizing autotrophic bacterium Nitrosomonas europaea, is shown to be a homo-oligomer of 12 kDa Cu-containing monomers. Oligonucleotides based on the amino acid sequence of the N-terminus and of the C-terminal tryptic peptide were used to sequence the gene by PCR. The translated protein sequence was significantly homologous with the mononuclear cupredoxins such as plastocyanin, azurin, or rusticyanin, the type 1 copper-binding region of
nitrite reductase
, and the binuclear CuA binding region of N(2)O reductase or cytochrome oxidase. The gene for NC contains a leader sequence indicating a periplasmic location. Optical bands for the red Cu center at 280, 390, 500, and 720 nm have extinction coefficients of 13.9, 7.0, 2.2, and 0.9 mM(-1), respectively. The reduction potential of NC (85 mV vs
SHE
) is much lower than those for known cupredoxins. Sequence alignments with homologous blue copper proteins suggested copper ligation by Cys95, His98, His103, and Glu60. Ligation by these residues (and a water), a trimeric protein structure, and a cupredoxin beta-barrel fold have been established by X-ray crystallography of the protein [Lieberman, R. L., Arciero, D. M., Hooper, A. B., and Rosenzweig, A. C. (2001) Biochemistry 40, 5674-5681]. EPR spectra of the red copper center indicated a Cu(II) species with a g(parallel) of 2.25 and an A(parallel) of 13.8 mT (144 x 10(-4) cm(-1)), typical of Cu in a type 2 copper environment. NC is the first example of a type 2 copper center in a cupredoxin fold. The open coordination site and type 2 copper suggest a possible catalytic rather than electron transfer function.
...
PMID:Nitrosocyanin, a red cupredoxin-like protein from Nitrosomonas europaea. 1182 13
Cytochrome
c
nitrite reductase
(ccNiR) is a periplasmic, decaheme homodimeric enzyme that catalyzes the six-electron reduction of nitrite to ammonia. Under standard assay conditions catalysis proceeds without detected intermediates, and it has been assumed that this is also true in vivo. However, this report demonstrates that it is possible to trap a putative intermediate by controlling the electrochemical potential at which reduction takes place. UV/vis spectropotentiometry showed that nitrite-loaded
Shewanella oneidensis
ccNiR is reduced in a concerted two-electron step to generate an {FeNO}
7
moiety at the active site, with an associated midpoint potential of +246 mV vs
SHE
at pH 7. By contrast, cyanide-bound active site reduction is a one-electron process with a midpoint potential of +20 mV, and without a strong-field ligand the active site midpoint potential shifts 70 mV lower still. EPR analysis subsequently revealed that the {FeNO}
7
moiety possesses an unusual spectral signature, different from those normally observed for {FeNO}
7
hemes, that may indicate magnetic interaction of the active site with nearby hemes. Protein film voltammetry experiments previously showed that catalytic nitrite reduction to ammonia by
S. oneidensis
ccNiR requires an applied potential of at least -120 mV, well below the midpoint potential for {FeNO}
7
formation. Thus, it appears that an {FeNO}
7
active site is a catalytic intermediate in the ccNiR-mediated reduction of nitrite to ammonia, whose degree of accumulation depends exclusively on the applied potential. At low potentials the species is rapidly reduced and does not accumulate, while at higher potentials it is trapped, thus preventing catalytic ammonia formation.
...
PMID:Trapping of a Putative Intermediate in the Cytochrome
c
Nitrite Reductase (ccNiR)-Catalyzed Reduction of Nitrite: Implications for the ccNiR Reaction Mechanism. 3138 4
