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Abstract: Rapid-scan FTIR difference spectroscopy was used to investigate proton and electron transfer reactions in photosynthetic reaction centers from Rhodobacter sphaeroides. Experiments at different temperatures and in the presence of D2O have provided strong indication that a transient band at 1707cm−1 previously identified after both the 1st and the 2nd flashes [A. Mezzetti, W. Leibl, Eur. Biophys. J. 34 (2005) 921] is given by a transient protonation of the side chain of a Asp or Glu residue situated on the proton transfer pathway from the cytoplasm to the QB site. Experiments in D2O on a Asp-M17→Asn mutant reaction center, where the proton and electron transfer reactions are slowed down compared to the wild-type, showed that the kinetic isotope effect induced by H/D exchange slows down the electron transfer reaction after the 1st flash, confirming the strong coupling between proton and electron transfer. Rapid-scan FTIR experiments on Cd2+-treated reaction centers, in agreement with previous UV–vis measurements [P. Adelroth, M.L. Paddock, L.B. Sagle, G. Feher, M.Y. Okamura, Proc. Natl. Acad. Sci. U.S.A. 97 (2000) 13086], showed that upon addition of Cd2+, which inhibits proton uptake, the QA −QB →QAQB − reaction is slowed. Interestingly, the transient 1707cm−1 band is not visible in the first spectrum recorded early after the flash. This strongly suggests its identification with a residue situated on the proton transfer pathway, which is perturbed upon metal cation binding. [Copyright &y& Elsevier]

Recently, the structure of a Cu-containing nitrite reductase (NiR) from Hyphomicrobium denitrificans ( HdNiR) has been reported, establishing the existence of a new family of Cu-NiR where an additional type 1 Cu (T1Cu) containing cupredoxin domain is located at the N-terminus (Nojiri et al. in Proc. Natl. Acad. Sci. USA 104:4315–4320, ). HdNiR retains the well-characterised coupled T1Cu–type 2 Cu (T2Cu) core, where the T2Cu catalytic site is also built utilising ligands from neighbouring monomers. We have undertaken a genome analysis and found the wide occurrence of these NiRs, with members clustering in two groups, one showing an amino acid sequence similarity of around 80% with HdNiR, and a second group, including the NiR from the extremophile Acidothermus cellulolyticus, clustering around 50% similarity to HdNiR. This is reminiscent of the difference observed between the blue ( Alcaligenes xylosoxidans) and green ( Achromobacter cycloclastes and Alcaligenes faecalis) NiRs which have been extensively studied and may indicate that these also form two distinct subclasses of the new family. Genome analysis also showed the presence of Cu-NiRs with a C-terminal extension of 160–190 residues containing a class I cytochrome c domain with a characteristic β-sheet extension. Currently no structural information exists for any member of this family. Genome analysis suggests the widespread occurrence of these novel NiRs with representatives in the α, β and γ subclasses of the Proteobacteria and in two species of the fungus Aspergillus. We selected the enzyme from Ralstonia pickettii for comparative modelling and produced a plausible structure highlighting an electron transfer mode in which the cytochrome c haem at the C-terminus can come within 16-Å reach of the T1Cu centre of the T1Cu–T2Cu core. [ABSTRACT FROM AUTHOR]

In this report we reported a facile one-pot method for synthesis of water-soluble and stable fluorescent CuNCs at room temperature, in which branched polyethyleneimine (BPEI) served as capping scaffold and ascorbic acid as reducing agent. The prepared BPEI-CuNCs exhibited excellent properties such as good water-solubility, photostability and high stability toward high ionic strength. Based on the electron transfer induced fluorescence quenching mechanism, this fluorescence probe was used for the sensitive and selective determination of ferric ions (Fe(3+)) in aqueous solution. The limit of detection was 340 nM in the linear range of 0.5-1000 μM, which was lower than the maximum level of Fe(3+) permitted in drinking water by the U.S. Environmental Protection Agency. The method was successfully applied to the detection of Fe(3+) in tap water, Yellow River water and human urine samples with the quantitative spike recoveries ranging from 95.3% to 112.0%., (Copyright © 2014 Elsevier B.V. All rights reserved.)