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  • 1
    ISSN: 1572-9729
    Keywords: biodegradation ; fluorophenols ; 19 F NMR ; oxidative defluorination ; Rhodococcus species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Of all NMR observable isotopes 19F is the one perhaps most convenient for studies on biodegradation of environmental pollutants. The reasons underlying this potential of 19F NMR are discussed and illustrated on the basis of a study on the biodegradation of fluorophenols by four Rhodococcus strains. The results indicate marked differences between the biodegradation pathways of fluorophenols among the various Rhodococcus species. This holds not only for the level and nature of the fluorinated biodegradation pathway intermediates that accumulate, but also for the regioselectivity of the initial hydroxylation step. Several of the Rhodococcus species contain a phenol hydroxylase that catalyses the oxidative defluorination of ortho-fluorinated di- and trifluorophenols. Furthermore, it is illustrated how the 19F NMR technique can be used as a tool in the process of identification of an accumulated unknown metabolite, in this case most likely 5-fluoromaleylacetate. Altogether, the 19F NMR technique proved valid to obtain detailed information on the microbial biodegradation pathways of fluorinated organics, but also to provide information on the specificity of enzymes generally considered unstable and, for this reason, not much studied so far.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5001
    Keywords: Triple-resonance 3D NMR ; Resonance assignments ; Chemical shifts ; Protein secondary structure ; Electron transfer ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The 1H, 15N and 13C backbone and 1H and 13C beta resonance assignments of the long-chain flavodoxin from Azotobacter chroococcum (the 20-kDa nifF product, flavodoxin-2) in its oxidized form were made at pH 6.5 and 30°C using heteronuclear multidimensional NMR spectroscopy. Analysis of the NOE connectivities, together with amide exchange rates, 3JHnHα coupling constants and secondary chemical shifts, provided extensive solution secondary structure information. The secondary structure consists of a five-stranded parallel β-sheet and five α-helices. One of the outer regions of the β-sheet shows no regular extended conformation, whereas the outer strand β4/6 is interrupted by a loop, which is typically observed in long-chain flavodoxins. Two of the five α-helices are nonregular at the N-terminus of the helix. Loop regions close to the FMN are identified. Negatively charged amino acid residues are found to be mainly clustered around the FMN, whereas a cluster of positively charged residues is located in one of the α-helices. Titration of the flavodoxin with the Fe protein of the A. chroococcum nitrogenase enzyme complex revealed that residues Asn11, Ser68 and Asn72 are involved in complex formation between the flavodoxin and Fe protein. The interaction between the flavodoxin and the Fe protein is influenced by MgADP and is of electrostatic nature.
    Type of Medium: Electronic Resource
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