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In Ralstonia eutropha H16, the nitric oxide (NO)-responsive transcriptional activator NorR controls the expression of a dicistronic operon that encodes a membrane-bound NO reductase, NorB, and a protein of unknown function, NorA. The N-terminal domain (NTD) of NorR is responsible for perception of the signal molecule, nitric oxide. Thirteen out of 29 conserved residues of the NTD were exchanged by site-directed mutagenesis. Replacement of R63, R72, D93, D96, C112, D130, or F137 strongly decreased NorR-dependent promoter activation, while the exchange of Y95 or H110 led to an increase in promoter activity compared to that of the wild type. A purified truncated NorR comprising only the NTD (NorR-NTD) contained one iron atom per molecule and was able to bind NO in the as-isolated state. Based on the iron content of NorR-NTD proteins with single amino acid replacements, residues R72, D93, D96, C112, and D130 are likely candidates for iron ligands. Residues R63, Y95, and H110 appear not to be involved in NO binding but may take part in subsequent steps of the signal transduction mechanism of NorR.The diatomic radical nitric oxide (NO) is an obligate intermediate of bacterial denitrification. NO is produced from nitrite by respiratory nitrite reductase and is converted to nitrous oxide by nitric oxide reductase (30). Also, nondenitrifiers like Escherichia coli K-12 can produce considerable amounts of NO during growth under hypoxic conditions with nitrate (6). Since NO and derived reactive nitrogen oxides act as toxic and mutagenic agents, defense mechanisms must be induced under conditions of nitrosative stress. NO-responsive transcription factors are found in the Fnr/Crp family (e.g., DnrD [31]), the Rrf2 family (e.g., NsrR [2]), and the NtrC/NifA family (e.g., NorR). The last protein has been identified in the betaproteobacterium Ralstonia eutropha H16 (21) and E. coli (15). However, genomic analysis revealed that NorR orthologs are widely distributed among beta-and gammaproteobacteria (22). Like all proteins of the 54 -dependent NtrC/NifA superfamily (25), NorR shows a typical modular structure, including an N-terminal domain (NTD), a central AAAϩ domain, and a helix-turn-helix domain for DNA binding (3,21). In a recent study, it was shown that the NTD of E. coli NorR harbors a mono-iron center that is able to bind NO as a ferrous nitrosyl (10). Those authors presented a model for the activation of NorR which postulates the existence of an inactive form of NorR, where the ATPase activity of the AAAϩ domain is blocked by the NTD. Upon binding of NO, this block is relieved and NorR switches to an active state which is competent to induce promoter activation. This hypothesis is corroborated by the fact that truncated forms of NorR from E. coli and R. eutropha that lack the NTD show signal-independent activation of gene expression (10, 21). To date, neither the iron ligands nor the residues that are involved in the switching mechanism have been identified.Given the high positional identity (45%) between the amino acid ...

(1) Background: To date, no information on the polishability of milled and 3D-printed complete denture bases has been provided, which is relevant in terms of plaque accumulation. (2) Methods: three groups (n = 30) were manufactured using the cold-polymerization polymethilmethacrilate, milling (SM) and 3D printing (AM). 10 specimens of each group were left untreated (reference). 10 more specimens were pre-polished (intermediate polishing) and 10 final specimens were highgloss polished. An additional 20 specimens were 3D printed and coated with the liquid resin (coated), 10 of which were additionally polished (coated + polished). For each group Ra and Rz values, gloss value and REM images were obtained. (3). The “highgloss-polished” specimens showed statistically lower Ra and Rz values in the SM, followed by AM and conventional groups. In the AM group statistically lower surfaces roughness was revealed for highgloss-polished, “coated + polished”, and “coated” specimens, respectively. (4) Conclusions: The milled specimens demonstrated superiors surface characteristics than 3D printed and conventionally produced after polishing. The polished specimens demonstrated superior surface characteristics over coated specimens. However, the surface roughness by both polished and coated specimens was within the clinically relevant threshold of 0.2 µm.