Nitrogenase Fe protein-like Fe–S cluster is conserved in L-protein (BchL) of dark-operative protochlorophyllide reductase from Rhodobacter capsulatus

AbstractDark-operative protochlorophyllide reductase (DPOR) in bacteriochlorophyll biosynthesis is a nitrogenase-like enzyme consisting of L-protein (BchL-dimer) as a reductase component and NB-protein (BchN–BchB-heterotetramer) as a catalytic component. Metallocenters of DPOR have not been identified. Here we report that L-protein has an oxygen-sensitive [4Fe–4S] cluster similar to nitrogenase Fe protein. Purified L-protein from Rhodobacter capsulatus showed absorption spectra and an electron paramagnetic resonance signal indicative of a [4Fe–4S] cluster. The activity quickly disappeared upon exposure to air with a half-life of 20s. These results suggest that the electron transfer mechanism is conserved in nitrogenase Fe protein and DPOR L-protein

Kinetics of NADP+/NADPH reduction–oxidation catalyzed by the ferredoxin-NAD(P)+ reductase from the green sulfur bacterium Chlorobaculum tepidum

Ferredoxin-NAD(P)+ oxidoreductase (FNR, [EC 1.18.1.2], [EC 1.18.1.3]) from the green sulfur bacterium Chlorobaculum tepidum (CtFNR) is a homodimeric flavoprotein with significant structural homology to bacterial NADPH-thioredoxin reductases. CtFNR homologs have been found in many bacteria, but only in green sulfur bacteria among photoautotrophs. In this work, we examined the reactions of CtFNR with NADP+, NADPH, and (4S-2H)-NADPD by stopped-flow spectrophotometry. Mixing CtFNRox with NADPH yielded a rapid decrease of the absorbance in flavin band I centered at 460 nm within 1 ms, and then the absorbance further decreased gradually. The magnitude of the decrease increased with increasing NADPH concentration, but even with ~50-fold molar excess NADPH, the absorbance change was only ~45 % of that expected for fully reduced protein. The absorbance in the charge transfer (CT) band centered around 600 nm increased rapidly within 1 ms, then slowly decreased to about 70 % of the maximum. When CtFNRred was mixed with excess NADP+, the absorbance in the flavin band I increased to about 70 % of that of CtFNRox with an apparent rate of ~4 s−1, whereas almost no absorption changes were observed in the CT band. Obtained data suggest that the reaction between CtFNR and NADP+/NADPH is reversible, in accordance with its physiological function. © 2016 Springer Science+Business Media DordrechtEmbargo period 12 month

Determinations of light spectrums under sea ice with fiber optics spectrometer

A fiber optics spectrophotometer (USB2000, OceanOptics, USA) was applied to measure light conditions under sea ice at Saroma-ko Lagoon, Hokkaido Japan, in February and March 2005. One end of a 10 m quartz fiber optics (QP200-2-UV-VIS, OceanOptics, USA) fixed under sea ice led light to the other end, and the spectrophotometer determined the spectrum of the light at the other end on the sea ice. Signals from the spectrophotometer were normalized with the calibration light source (DH2000CAL, OceanOptics, USA) and a program (OOIBase, OOIIrad, OceanOptics, USA) and were determined as irradiance (w m^ mn^). Without the cosine-collector for collecting the light from 180 degrees in front, the fiber optics collected light from a narrow range and showed quite different spectrums from those determined with the cosine-collector. Spectrums with a peak at 570 nm were determined with the cosine-collector and corresponded well with the spectrums often determined at near coastal areas. Photon flux densities (μmol photons s^m^ nm^) were estimated from spectrums determined with the cosine-collector and correlated well (R^2=0.98) with those determined with the quantum sensor (LI-193, LI-COR, USA). These results showed that fiber optics spectrophotometer could determine the light conditions under sea ice both qualitatively and quantitatively

Rubredoxin from the green sulfur bacterium Chlorobaculum tepidum donates a redox equivalent to the flavodiiron protein in an NAD(P)H dependent manner via ferredoxin-NAD(P)+ oxidoreductase

金沢大学理工研究域物質化学系The green sulfur bacterium, Chlorobaculum tepidum, is an anaerobic photoautotroph that performs anoxygenic photosynthesis. Although genes encoding rubredoxin (Rd) and a putative flavodiiron protein (FDP) were reported in the genome, a gene encoding putative NADH-Rd oxidoreductase is not identified. In this work, we expressed and purified the recombinant Rd and FDP and confirmed dioxygen reductase activity in the presence of ferredoxin-NAD(P)+ oxidoreductase (FNR). FNR from C. tepidum and Bacillus subtilis catalyzed the reduction of Rd at rates comparable to those reported for NADH-Rd oxidoreductases. Also, we observed substrate inhibition at high concentrations of NADPH similar to that observed with ferredoxins. In the presence of NADPH, B. subtilis FNR and Rd, FDP promoted dioxygen reduction at rates comparable to those reported for other bacterial FDPs. Taken together, our results suggest that Rd and FDP participate in the reduction of dioxygen in C. tepidum and that FNR can promote the reduction of Rd in this bacterium.This work was partly supported by Japan Society for the Promotion of Science KAKENHI Grant Number JP17K07304 (to DS) and JP18K06296 (to KI). AcknowledgementsEmbargo Period 12 month

Correction: Sakurai, H.; et al. How Close We Are to Achieving Commercially Viable Large-Scale Photobiological Hydrogen Production by Cyanobacteria: A Review of the Biological Aspects. Life 2015, 5, 997–1018

In the published article “How close we are to achieving commercially viable large-scale photobiological hydrogen production by cyanobacteria:[...

How Close We Are to Achieving Commercially Viable Large-Scale Photobiological Hydrogen Production by Cyanobacteria: A Review of the Biological Aspects

Photobiological production of H2 by cyanobacteria is considered to be an ideal source of renewable energy because the inputs, water and sunlight, are abundant. The products of photobiological systems are H2 and O2; the H2 can be used as the energy source of fuel cells, etc., which generate electricity at high efficiencies and minimal pollution, as the waste product is H2O. Overall, production of commercially viable algal fuels in any form, including biomass and biodiesel, is challenging, and the very few systems that are operational have yet to be evaluated. In this paper we will: briefly review some of the necessary conditions for economical production, summarize the reports of photobiological H2 production by cyanobacteria, present our schemes for future production, and discuss the necessity for further progress in the research needed to achieve commercially viable large-scale H2 production

Magnetic and Electrochemical Properties of Lantern-Type Dinuclear Ru(II,III) Complexes with Axial Chloride Ions or Water Molecules

By using [Ru2(O2CC3H7)4Cl]n (1) as a starting material, nBu4N[Ru2(O2CC3H7)4Cl2] (nBu4N+ = tetra(n-butyl)ammonium cation) (2) and [Ru2(O2CC3H7)4(H2O)2]BF4 (3) were prepared. The lantern-type dinuclear structures with axial chloride ions or water molecules were confirmed for 2 and 3 by X-ray crystal structure analyses. The crystal structures of 2 and 3 were compared with that of 1. In the crystal of 2, there were three crystallographically different dinuclear units; the Ru–Ru distances of each unit were 2.3094(3), 2.3046(4), and 2.3034(4) Å, respectively, which were longer than those of 1 (2.281(4) Å) and 3 (2.2584 (7) Å). Temperature dependent magnetic susceptibility measurements were performed for 1 and 2 as well as 3. The effective magnetic moments (µeff) at 300 K were 3.97 (for 1), 4.00 (for 2), and 3.97 µB (for 3), respectively. The decreases in the µeff value were confirmed for all of the complexes due to the large zero-field splitting (D): D = 68 cm−1 for 1, 78 cm−1 for 2, and 60 cm−1 for 3. Cyclic voltammograms measured in CH2Cl2 with a electrolyte of nBu4N(BF4) showed the Ru25+/Ru24+ process at −0.2–−0.4 V (vs. SCE) and the Ru26+/Ru25+ one at 1.3–1.4 V (vs. SCE), of which potentials were confirmed by the DFT calculation for nBu4N[Ru2(O2CC3H7)4Cl2]