Insights from 125Te and 57Fe nuclear resonance vibrational spectroscopy: a [4Fe-4Te] cluster from two points of view.

Iron-sulfur clusters are common building blocks for electron transport and active sites of metalloproteins. Their comprehensive investigation is crucial for understanding these enzymes, which play important roles in modern biomimetic catalysis and biotechnology applications. We address this issue by utilizing (Et4N)3[Fe4Te4(SPh)4], a tellurium modified version of a conventional reduced [4Fe-4S]+ cluster, and performed both 57Fe- and 125Te-NRVS to reveal its characteristic vibrational features. Our analysis exposed major differences in the resulting 57Fe spectrum profile as compared to that of the respective [4Fe-4S] cluster, and between the 57Fe and 125Te profiles. DFT calculations are applied to rationalize structural, electronic, vibrational, and redox-dependent properties of the [4Fe-4Te]+ core. We herein highlight the potential of sulfur/tellurium exchange as a method to isolate the iron-only motion in enzymatic systems

Characterization of a synthetic peroxodiiron(III) protein model complex by nuclear resonance vibrational spectroscopy

The vibrational spectrum of an η[superscript 1],η[superscript 1]-1,2-peroxodiiron(III) complex was measured by nuclear resonance vibrational spectroscopy and fit using an empirical force field analysis. Isotopic 18O2 labelling studies revealed a feature involving motion of the {Fe2(O2)}[superscript 4+] core that was not previously observed by resonance Raman spectroscopy.National Institute of General Medical Sciences (U.S.) (GM-032134

Journal of Electron Spectroscopy and Related Phenomena 143 (2005) 1-7 X-ray absorption spectroscopy of biological photolysis products: kilohertz photolysis and soft X-ray applications

Abstract In this study, we report the first kilohertz laser photolysis of carbonmonoxy myoglobin (MbCO), studied by hard X-ray absorption spectroscopy (XAS, iron K-edge at ∼7 keV). In addition, traditional frozen photolysis of MbCO has also been evaluated, alternatively, with soft X-ray absorption spectroscopy (iron L-edge at <1 keV). Changes in the K absorption edge position, the pre-K 1s-3d feature and the K-edge XANES spectra have been clearly observed following the photodissociation of MbCO, which shows the structural/electronic changes in between MbCO and its photolysis product Mb*CO, and demonstrates the advanced capacities of our apparatus in monitoring and/or characterizing biological photolysis products. On the other hand, the iron L-edge XAS have shown clearer differences (than K-edge XAS) on the electronic information between the bound MbCO and the photolyzed Mb*CO. The results from these two approaches have been compared and discussed. Practical issues related to the use of kilohertz laser with biological samples, and with synchrotron radiation beamlines, have also been discussed

Enzymatic and spectroscopic properties of a thermostable [NiFe]‑hydrogenase performing H2-driven NAD+-reduction in the presence of O2

Biocatalysts that mediate the H2-dependent reduction of NAD+ to NADH are attractive from both a fundamental and applied perspective. Here we present the first biochemical and spectroscopic characterization of an NAD+-reducing [NiFe]‑hydrogenase that sustains catalytic activity at high temperatures and in the presence of O2, which usually acts as an inhibitor. We isolated and sequenced the four structural genes, hoxFUYH, encoding the soluble NAD+-reducing [NiFe]‑hydrogenase (SH) from the thermophilic betaproteobacterium, Hydrogenophilus thermoluteolus TH-1T (Ht). The HtSH was recombinantly overproduced in a hydrogenase-free mutant of the well-studied, H2-oxidizing betaproteobacterium Ralstonia eutropha H16 (Re). The enzyme was purified and characterized with various biochemical and spectroscopic techniques. Highest H2-mediated NAD+ reduction activity was observed at 80 °C and pH 6.5, and catalytic activity was found to be sustained at low O2 concentrations. Infrared spectroscopic analyses revealed a spectral pattern for as-isolated HtSH that is remarkably different from those of the closely related ReSH and other [NiFe]‑hydrogenases. This indicates an unusual configuration of the oxidized catalytic center in HtSH. Complementary electron paramagnetic resonance spectroscopic analyses revealed spectral signatures similar to related NAD+-reducing [NiFe]‑hydrogenases. This study lays the groundwork for structural and functional analyses of the HtSH as well as application of this enzyme for H2-driven cofactor recycling under oxic conditions at elevated temperatures

Synthesis and vibrational spectroscopy of Fe-57-labeled models of [NiFe] hydrogenase: first direct observation of a nickel-iron interaction

A new route to iron carbonyls has enabled synthesis of 57Fe-​labeled [NiFe] hydrogenase mimic (OC)​357Fe(pdt)​Ni(dppe) (pdt = 1,​3-​propanedithiolate)​. Its study by nuclear resonance vibrational spectroscopy revealed Ni-​57Fe vibrations, as confirmed by calcns. The modes are absent for [(OC)​357Fe(pdt)​Ni(dppe)​]​+, which lacks Ni-​57Fe bonding, underscoring the utility of the analyses in identifying metal-​metal interactions

X-ray Magnetic Circular Dichroism of Pseudomonas aeruginosa Nickel(II) Azurin

We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L3-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) μ_B. Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d_x^2-y^2 and 3d_z^2 are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d_x^2_(-y)^2 having much greater ligand character

Real sample temperature: a critical issue in the experiments of nuclear resonant vibrational spectroscopy on biological samples

NIH [GM-65440, EB-001962]; DOE Office of Biological and Environmental Research; JASRI; JST (CREST); [ESRF/ID18]; [APS/03ID]There are several practical and intertangled issues which make the experiments of nuclear resonant vibrational spectroscopy (NRVS) on biological samples difficult to perform. The sample temperature is one of the most important issues. In NRVS the real sample temperatures can be very different from the readings on the temperature sensors. In this study the following have been performed: (i) citing and analyzing various existing NRVS data to assess the real sample temperatures during the NRVS measurements and to understand their trends with the samples' loading conditions; (ii) designing several NRVS measurements with (Et4N)[FeCl4] to verify these trends; and (iii) proposing a new sample-loading procedure to achieve significantly lower real sample temperatures and to balance among the intertangled experimental issues in biological NRVS measurements

Redox, haem and CO in enzymatic catalysis and regulation

The present paper describes general principles of redox catalysis and redox regulation in two diverse systems. The first is microbial metabolism of CO by the Wood–Ljungdahl pathway, which involves the conversion of CO or H2/CO2 into acetyl-CoA, which then serves as a source of ATP and cell carbon. The focus is on two enzymes that make and utilize CO, CODH (carbon monoxide dehydrogenase) and ACS (acetyl-CoA synthase). In this pathway, CODH converts CO2 into CO and ACS generates acetyl-CoA in a reaction involving Ni·CO, methyl-Ni and acetyl-Ni as catalytic intermediates. A 70 Å (1 Å=0.1 nm) channel guides CO, generated at the active site of CODH, to a CO ‘cage’ near the ACS active site to sequester this reactive species and assure its rapid availability to participate in a kinetically coupled reaction with an unstable Ni(I) state that was recently trapped by photolytic, rapid kinetic and spectroscopic studies. The present paper also describes studies of two haem-regulated systems that involve a principle of metabolic regulation interlinking redox, haem and CO. Recent studies with HO2 (haem oxygenase-2), a K+ ion channel (the BK channel) and a nuclear receptor (Rev-Erb) demonstrate that this mode of regulation involves a thiol–disulfide redox switch that regulates haem binding and that gas signalling molecules (CO and NO) modulate the effect of haem.National Institutes of Health (U.S.) (NIH grant GM69857)National Institutes of Health (U.S.) (NIH grant GM39451)National Institutes of Health (U.S.) (NIH grant HL 102662)National Institutes of Health (U.S.) (NIH grant GM65440)National Institutes of Health (U.S.) (NIH grant GM48242)National Institutes of Health (U.S.) (NIH grant Y1-GM- 1104)National Institutes of Health (U.S.) (NIH grant GM065318)National Institutes of Health (U.S.) (NIH grant AG027349)National Science Foundation (U.S.) (grant number CHE-0745353)United States. Dept. of Energy. Office of Biological and Environmental ResearchHoward Hughes Medical Institute (Investigator

Unconditional positive self-regard, intrinsic aspirations and authenticity: pathways to psychological well-being

Unconditional positive self-regard (UPSR) is regarded by humanistic psychologists as an important determinant of well-being. However, until recently it has received little empirical attention. The current study aims to examine the association between unconditional positive self-regard and several key constructs consistent with the ideas of well-being within contemporary positive psychology. Study 1 is a confirmatory factor analysis of the UPSR scale. The statistically significant best fit for the data was a related two-factor model. Study 2 used the two-factors of the UPSR scale to explore the association with intrinsic aspirations. The study showed positive self-regard was statistically significantly positively correlated with the intrinsic aspirations total scale and with each of the separate scores for IA-importance and IA-chance. Unconditionality of regard was statistically significantly negatively correlated with IA-importance but was not statistically significantly correlated to either the IA-total or IA-chance scores. Study 3 considers the association between UPSR, intrinsic aspirations and authenticity. Unconditionality of regard was statistically significantly positively correlated with the authenticity scale score. Only IA-chance scores showed a statistically significant and positive correlation with authenticity. The remaining correlations between intrinsic aspirations and authenticity were not statistically significant. Results call for further empirical attention to UPSR within positive psychology research