Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.4 (nitrite reductase)
 1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Oxygen caused a reversible inhibition (switch-off) of nitrogenase activity in whole cells of four strains of diazotrophs, the facultative anaerobe Klebsiella pneumoniae and three strains of photosynthetic bacteria (Rhodopseudomonas sphaeroides f. sp. denitrificans and Rhodopseudomonas capsulata strains AD2 and BK5). In K. pneumoniae 50% inhibition of acetylene reduction was attained at an O2 concentration of 0.37 microM. Cyanide (90 microM), which did not affect acetylene reduction but inhibited whole-cell respiration by 60 to 70%, shifted the O2 concentration that caused 50% inhibition of nitrogenase activity to 2.9 microM. A mutant strain of K. pneumoniae, strain AH11, has a respiration rate that is 65 to 75% higher than that of the wild type, but its nitrogenase activity is similar to wild-type activity. Acetylene reduction by whole cells of this mutant was inhibited 50% by 0.20 microM O2. Inhibition by CN- of 40 to 50% of the O2 uptake in the mutant shifted the O2 concentration that caused 50% inhibition of nitrogenase to 1.58 microM. Thus, when the respiration rates were lower, higher oxygen concentrations were required to inhibit nitrogenase. Reversible inhibition of nitrogenase activity in vivo was caused under anaerobic conditions by other electron acceptors. Addition of 2 mM sulfite to cell suspensions of R. capsulata B10 and R. sphaeroides inhibited nitrogenase activity. Nitrite also inhibited acetylene reduction in whole cells of the photodenitrifier R. sphaeroides but not in R. capsulata B10, which is not capable of enzymatic reduction of NO2-. Lower concentrations of NO2- were required to inhibit the activity in NO3- -grown cells, which have higher activities of nitrite reductase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mechanism of nitrogenase switch-off by oxygen. 354 74

Neuroglobin (Ngb) is a six-coordinate globin that can catalyze the reduction of nitrite to nitric oxide. Although this reaction is common to heme proteins, the molecular interactions in the heme pocket that regulate this reaction are largely unknown. We have shown that the H64L Ngb mutation increases the rate of nitrite reduction by 2000-fold compared to that of wild-type Ngb [Tiso, M., et al. (2011) J. Biol. Chem. 286, 18277-18289]. Here we explore the effect of distal heme pocket mutations on nitrite reduction. For this purpose, we have generated mutations of Ngb residues Phe28(B10), His64(E7), and Val68(E11). Our results indicate a dichotomy in the reactivity of deoxy five- and six-coordinate globins toward nitrite. In hemoglobin and myoglobin, there is a correlation between faster rates and more negative potentials. However, in Ngb, reaction rates are apparently related to the distal pocket volume, and redox potential shows a poor relationship with the rate constants. This suggests a relationship between the nitrite reduction rate and heme accessibility in Ngb, particularly marked for His64(E7) mutants. In five-coordinate globins, His(E7) facilitates nitrite reduction, likely through proton donation. Conversely, in Ngb, the reduction mechanism does not rely on the delivery of a proton from the histidine side chain, as His64 mutants show the fastest reduction rates. In fact, the rate observed for H64A Ngb (1120 M(-1) s(-1)) is to the best of our knowledge the fastest reported for a heme nitrite reductase. These differences may be related to a differential stabilization of the iron-nitrite complexes in five- and six-coordinate globins.
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PMID:Exploring the mechanisms of the reductase activity of neuroglobin by site-directed mutagenesis of the heme distal pocket. 2605 90