Molybdenum x-ray absorption edge spectra. The chemical state of molybdenum in nitrogenase

Cramer, Stephen P.; Eccles, T. K.; Kutzler, Frank W.; Hodgson, Keith O.; Mortenson, Leonard E.

doi:10.1021/ja00421a053

Cited by 116 publications

(81 citation statements)

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“…For example, a comparison of the copper k-edge spectra of oxy and deoxy forms of P. interruptus Hc (Fig. 5), a very close homolog of C. aestuarii Hc, indicates a shift of 2-3 eV to higher energy expected from the increase in the 1s-electron binding energy for the metal ion in the oxy protein because of its cupric character (14). The difference spectrum between deoxy and oxyHc allows for an accurate determination of the peak positions in the edge spectra of the deoxy protein.…”

Section: Resultsmentioning

confidence: 99%

“…For Cu(I), a species with limited potential for other spectroscopic studies as it lacks color and paramagnetism, coordination geometry can be deduced from copper k-edge absorbance measurements. Previous studies on Cu(I) model complexes of known structure provide the background information used to define a correlation between k-edge features and coordination geometry (14,15).…”

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confidence: 99%

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Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

Hirota

Kawahara

Beltramini

et al. 2008

Journal of Biological Chemistry

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Flash photolysis and K-edge x-ray absorption spectroscopy (XAS) were used to investigate the functional and structural effects of pH on the oxygen affinity of three homologous arthropod hemocyanins (Hcs). Flash photolysis measurements showed that the well-characterized pH dependence of oxygen affinity (Bohr effect) is attributable to changes in the oxygen binding rate constant, k on , rather than changes in k off . In parallel, coordination geometry of copper in Hc was evaluated as a function of pH by XAS. It was found that the geometry of copper in the oxygenated protein is unchanged at all pH values investigated, while significant changes were observed for the deoxygenated protein as a function of pH. The interpretation of these changes was based on previously described correlations between spectral lineshape and coordination geometry obtained for model compounds of known structure (Blackburn, N. J., Strange, R. W., Reedijk, J., Volbeda, A., Farooq, A., Karlin, K. D., and Zubieta, J. (1989) Inorg. Chem., 28, 1349 -1357). A pH-dependent change in the geometry of cuprous copper in the active site of deoxyHc, from pseudotetrahedral toward trigonal was assigned from the observed intensity dependence of the 1s 3 4p z transition in x-ray absorption near edge structure (XANES) spectra. The structural alteration correlated well with increase in oxygen affinity at alkaline pH determined in flash photolysis experiments. These results suggest that the oxygen binding rate in deoxyHc depends on the coordination geometry of Cu(I) and suggest a structural origin for the Bohr effect in arthropod Hcs. Hemocyanins (Hcs)3 are oxygen carrier and storage proteins found in molluscs and arthropods. Significant differences are observed between mollusc and arthropod Hcs in size of the functional units and in their tertiary and quaternary structures. Specifically, arthropod Hcs are structurally homogenous oligomeric proteins with a minimal functional subunit of 75 kDa. Under physiological conditions in the presence of calcium, the subunits are typically arranged in hexamers and dodecamers. Removal of Ca 2ϩ with EDTA at neutral pH causes dissociation of the dodecamer into hexamers, which can be dissociated into monomers at alkaline pH (1). The different aggregation states are related to modified oxygen binding properties (2). As generally observed for respiratory proteins, a fundamental physiological property of Hc is its competence to bind oxygen with different affinity in response to allosteric effectors including hydrogen ions.Detailed structural information concerning the active site of Hcs is derived mainly from a limited set of x-ray crystallographic investigations. The active site structures of the deoxy form have been described for two arthropod Hcs, Panulirus interruptus (3) and Limulus polyphemus (subunit II) (4). However, a comparison of the results is limited by the different solution conditions from which the proteins were crystallized. In both examples, each Cu(I) of the binuclear active site is coordinated by the ⑀-nitrog...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

Hirota

Kawahara

Beltramini

et al. 2008

Journal of Biological Chemistry

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“…X-ray absorption near-edge structure (XANES) spectroscopy is the most well-known of these techniques and has been extensively used in the field of metalloproteins to investigate the oxidation states of redoxactive metals in metalloprotein active sites. [42][43][44][45][46][47][48][49][50][51] The principal component in XANES spectra is a 1s → 4p absorption edge in Mn. The pioneering application of XANES to PS II was performed by Goodin et al in the early 1980s.…”

Section: Introductionmentioning

confidence: 99%

Absence of Mn-Centered Oxidation in the S₂→ S₃Transition: Implications for the Mechanism of Photosynthetic Water Oxidation

et al. 2001

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A key question for the understanding of photosynthetic water oxidation is whether the four oxidizing equivalents necessary to oxidize water to dioxygen are accumulated on the four Mn ions of the oxygen-evolving complex (OEC), or whether some ligand-centered oxidations take place before the formation and release of dioxygen during the S 3 → [S 4 ] → S 0 transition. Progress in instrumentation and flash sample preparation allowed us to apply Mn Kβ X-ray emission spectroscopy (Kβ XES) to this problem for the first time. The Kβ XES results, in combination with Mn X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) data obtained from the same set of samples, show that the S 2 → S 3 transition, in contrast to the S 0 → S 1 and S 1 → S 2 transitions, does not involve a Mn-centered oxidation. On the basis of new structural data from the S 3 -state, manganese μ-oxo bridge radical formation is proposed for the S 2 → S 3 transition, and three possible mechanisms for the O-O bond formation are presented.

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“…Figure 15 shows is smaller than anticipated. Reduced edge shift due to higher covalency of the metal-ligand bonds has been observed in several other cases [35,36]. The concept of coordination charge,…”

Section: Incorporation Of Cerium Into Nickel Oxide Filmsmentioning

confidence: 93%

“…where the formal charge of a metal is reduced by a factor corresponding to the degree of covalency of the bonding ligand, has been employed to explain differences in absorption edge shifts [35,36]. Further evidence for the increase in the oxidation state of Fe in the codeposited film on anodic oxidation in KOH can be obtained by analyzing the EXAFS spectra.…”

Section: Incorporation Of Cerium Into Nickel Oxide Filmsmentioning

confidence: 99%

``In-situ'' spectro-electrochemical studies of radionuclide-contaminated surface films on metals

Melendres¹,

Mini²,

Mansour³

2000

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Molybdenum x-ray absorption edge spectra. The chemical state of molybdenum in nitrogenase

Cited by 116 publications

References 0 publications

Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

Absence of Mn-Centered Oxidation in the S₂→ S₃Transition: Implications for the Mechanism of Photosynthetic Water Oxidation

``In-situ'' spectro-electrochemical studies of radionuclide-contaminated surface films on metals

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Molybdenum x-ray absorption edge spectra. The chemical state of molybdenum in nitrogenase

Cited by 116 publications

References 0 publications

Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

Absence of Mn-Centered Oxidation in the S2→ S3Transition: Implications for the Mechanism of Photosynthetic Water Oxidation

``In-situ'' spectro-electrochemical studies of radionuclide-contaminated surface films on metals

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Absence of Mn-Centered Oxidation in the S₂→ S₃Transition: Implications for the Mechanism of Photosynthetic Water Oxidation