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M P Klein

Publications and source records attributed to M P Klein.

At least 19 recordsLinked to original sources
PubMed2001

Absence of Mn-centered oxidation in the S(2) --> S(3) transition: implications for the mechanism of photosynthetic water oxidation.

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 Kbeta X-ray emission spectroscopy (Kbeta XES) to this problem for the first time. The Kbeta 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 mu-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.

Electron Spin Resonance Spectroscopy↗
PubMed2001

Mn K-edge XANES and Kbeta XES studies of two Mn-oxo binuclear complexes: investigation of three different oxidation states relevant to the oxygen-evolving complex of photosystem II.

Two structurally homologous Mn compounds in different oxidation states were studied to investigate the relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edge structure (XANES) and Mn Kbeta X-ray emission spectroscopy (Kbeta XES). The two manganese compounds are the di-mu-oxo compound [L'2Mn(III)O2Mn(IV)L'2](ClO4)3, where L' is 1,10-phenanthroline (Cooper, S. R.; Calvin, M. J. Am. Chem. Soc. 1977, 99, 6623-6630) and the linear mono-mu-oxo compound [LMn(III)OMn(III)L](ClO4)2, where L- is the monoanionic N,N-bis(2-pyridylmethyl)-N'-salicylidene-1,2-diaminoethane ligand (Horner, O.; Anxolabéhère-Mallart, E.; Charlot, M. F.; Tchertanov, L.; Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd, J.-J. Inorg. Chem. 1999, 38, 1222-1232). Preparative bulk electrolysis in acetonitrile was used to obtain higher oxidation states of the compounds: the Mn(IV)Mn(IV) species for the di-mu-oxo compound and the Mn(III)Mn(IV) and Mn(IV)Mn(IV) species for the mono-mu-oxo compound. IR, UV/vis, EPR, and EXAFS spectra were used to determine the purity and integrity of the various sample solutions. The Mn K-edge XANES spectra shift to higher energy upon oxidation when the ligand environment remains similar. However, shifts in energy are also observed when only the ligand environment is altered. This is achieved by comparing the di-mu-oxo and linear mono-mu-oxo Mn-Mn moieties in equivalent oxidation states, which represent major structural changes. The magnitude of an energy shift due to major changes in ligand environment can be as large as that of an oxidation-state change. Therefore, care must be exercised when correlating the Mn K-edge energies to manganese oxidation states without taking into account the nature of the ligand environment and the overall structure of the compound. In contrast to Mn K-edge XANES, Kbeta XES spectra show less dependence on ligand environment. The Kbeta1,3 peak energies are comparable for the di-mu-oxo and mono-mu-oxo compounds in equivalent oxidation states. The energy shifts observed due to oxidation are also similar for the two different compounds. The study of the different behavior of the XANES pre-edge and main-edge features in conjunction with Kbeta XES provides significant information about the oxidation state and character of the ligand environment of manganese atoms.

Electrochemistry↗
PubMed2001

High-resolution X-ray spectroscopy of rare events: a different look at local structure and chemistry.

The combination of large-acceptance high-resolution X-ray optics with bright synchrotron sources permits quantitative analysis of rare events such as X-ray fluorescence from very dilute systems, weak fluorescence transitions or X-ray Raman scattering. Transition-metal Kbeta fluorescence contains information about spin and oxidation state; examples of the characterization of the Mn oxidation states in the oxygen-evolving complex of photosystem II and Mn-consuming spores from the marine bacillus SG- are presented. Weaker features of the Kbeta spectrum resulting from valence-level and 'interatomic' ligand to metal transitions contain detailed information on the ligand- atom type, distance and orientation. Applications of this spectral region to characterize the local structure of model compounds are presented. X-ray Raman scattering (XRS) is an extremely rare event, but also represents a unique technique to obtain bulk-sensitive low-energy (<600 eV) X-ray absorption fine structure (XAFS) spectra using hard (approximately 10 keV) X-rays. A photon is inelastically scattered, losing part of its energy to promote an electron into an unoccupied level. In many cases, the cross section is proportional to that of the corresponding absorption process yielding the same X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) features. XRS finds application for systems that defy XAFS analysis at low energies, e.g. liquids or highly concentrated complex systems, reactive compounds and samples under extreme conditions (pressure, temperature). Recent results are discussed.

Bacillus↗
PubMed1998

Sulfur K-edge x-ray absorption spectroscopy: a spectroscopic tool to examine the redox state of S-containing metabolites in vivo.

The sulfur K-edge x-ray absorption spectra for the amino acids cysteine and methionine and their corresponding oxidized forms cystine and methionine sulfoxide are presented. Distinct differences in the shape of the edge and the inflection point energy for cysteine and cystine are observed. For methionine sulfoxide the inflection point energy is 2.8 eV higher compared with methionine. Glutathione, the most abundant thiol in animal cells, also has been investigated. The x-ray absorption near-edge structure spectrum of reduced glutathione resembles that of cysteine, whereas the spectrum of oxidized glutathione resembles that of cystine. The characteristic differences between the thiol and disulfide spectra enable one to determine the redox status (thiol to disulfide ratio) in intact biological systems, such as unbroken cells, where glutathione and cyst(e)ine are the two major sulfur-containing components. The sulfur K-edge spectra for whole human blood, plasma, and erythrocytes are shown. The erythrocyte sulfur K-edge spectrum is similar to that of fully reduced glutathione. Simulation of the plasma spectrum indicated 32% thiol and 68% disulfide sulfur. The whole blood spectrum can be simulated by a combination of 46% disulfide and 54% thiol sulfur.

Erythrocytes↗
PubMed1997

Fiber transformations in multifidus muscle of young patients with idiopathic scoliosis.

STUDY DESIGN: In this study, the authors investigated the superficial multifidus muscle in patients with idiopathic scoliosis. During spinal fusion, biopsies were taken bilaterally at the apex of the curve, and at the upper and lower end vertebrae. OBJECTIVES: To analyze the muscular reactions in response to bracing in patients with idiopathic scoliosis. SUMMARY OF BACKGROUND DATA: The extent to which intervertebral mobility is restricted by an orthosis is still controversial. In addition, the effect of bracing on the erector spinae has not been investigated. METHODS: Of a total 30 patients, 11 had been treated with a corset for a year or more before surgery. Biopsies were investigated histochemically and the muscle fibers classified as Type I, IIA, IIB, or IIC (transitional fibers). The relative distribution of the fibers was calculated and their diameter was measured. RESULTS: In unbraced patients, a shift in the fiber distribution (from "slow" to "fast") was observed exclusively at the concave side of the apex. This shift was paralleled by an increased percentage of the intermediate Type IIC fiber (indicative of fiber transformation). In patients who always wore a corset, the relative amount of Type IIC fibers was increased, without preference for a specific location. CONCLUSIONS: Corset treatment elicits muscle fiber transformation processes at different levels along the scoliosis. This general reaction of the paraspinal muscles provides strong evidence against the existence of muscular disorders that are restricted to the area of the apex and are thus causing the scoliosis. As such, it must be assumed that the muscular changes in the apical region are secondary.

Adenosine Triphosphate↗
PubMed1996

Oxidation states of the manganese cluster during the flash-induced S-state cycle of the photosynthetic oxygen-evolving complex.

The Mn K-edge x-ray absorption spectra for the pure S states of the tetranuclear Mn cluster of the oxygen-evolving complex of photosystem II during flash-induced S-state cycling have been determined. The relative S-state populations in samples given 0, 1, 2, 3, 4, or 5 flashes were determined from fitting the flash-induced electron paramagnetic resonance (EPR) multiline signal oscillation pattern to the Kok model. The edge spectra of samples given 0, 1, 2, or 3 flashes were combined with EPR information to calculate the pure S-state edge spectra. The edge positions (defined as the zero-crossing of the second derivatives) are 6550.1, 6551.7, 6553.5, and 6553.8 eV for S0, S1, S2, and S3, respectively. In addition to the shift in edge position, the S0--> S1 and S1--> S2 transitions are accompanied by characteristic changes in the shape of the edge, both indicative of Mn oxidation. The edge position shifts very little (0.3 eV) for the S2--> S3 transition, and the edge shape shows only subtle changes. We conclude that probably no direct Mn oxidation is involved in this transition. The proposed Mn oxidation state assignments are as follows: S0 (II, III, IV, IV) or (III, III, III, IV), S1 (III, III, IV, IV), S2 (III, IV, IV, IV), S3 (III, IV, IV, IV).

Journal Article↗
PubMed1995

Spin-labeled psoralen probes for the study of DNA dynamics.

Six nitroxide spin-labeled psoralen derivative have been synthesized and evaluated as probes for structural and dynamic studies. Sequence specific photoaddition of these derivatives to DNA oligonucleotides resulted in site-specifically cross-linked and spin-labeled oligomers. Comparison of the general line shape features of the observed electron paramagnetic resonance (EPR) spectra of several duplexes ranging in size from 8 to 46 base pairs with simulated EPR spectra indicate that the nitroxide spin-label probe reports the global tumbling motion of the oligomers. While there is no apparent large amplitude motion of the psoralen other than the overall tumbling of the DNA on the time scales investigated, there are some indications of bending and other residual motions. The (A)BC excinuclease DNA repair system detects structural or dynamic features of the DNA that distinguish between damaged and undamaged DNA and are independent of the intrinsic structure of the lesion. NMR studies have shown that psoralen-cross-linked DNA has altered backbone dynamics and conformational populations in the immediate vicinity of the adduct [Emsley et al. (1993) J. Am. Chem. Soc. 115, 7765-7771; Spielmann et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 2345-2349]. We suggested that the signal for recognition of a lesion to be repaired is in the sugar--phosphate backbone and not in the damaged base(s).

Base Sequence↗
PubMed1995

Evidence for the proximity of calcium to the manganese cluster of photosystem II: determination by X-ray absorption spectroscopy.

The photosynthetic oxygen-evolving complex contains a cluster of four manganese atoms and requires both Ca and Cl for activity. The question of Ca proximity to the Mn cluster has been investigated by performing Mn X-ray absorption experiments on native samples of photosystem II (PS II) and on samples depleted of Ca and reconstituted by either Ca or Sr. Analysis of X-ray K-edge spectra demonstrates no significant differences in oxidation state or symmetry between Ca- and Sr-reactivated preparations. Differences are observed in the extended X-ray absorption fine structure (EXAFS). The amplitude of a Fourier transform peak due to scatters at distances greater than 3 A is larger for samples reactivated with strontium than for calcium-reactivated samples. Taking into account the stoichiometry of Mn and Ca atoms in PS II, and considering physically reasonable structures, curve-fitting analyses of the EXAFS data using FEFF5-calculated parameters favor a model where both manganese and calcium (or strontium) scatterers contribute to the Fourier peak at approximately 3 A. Other models for the approximately 3 A peak with multiple Mn-Mn interactions or multiple Mn-Ca(Sr) interactions can also be fit to the data, but are considered less likely. This result provides confirmation for the structural proximity of Ca to the Mn cluster suggested previously [Yachandra, V. K., et al. (1993) Science 260, 675-679]. Possible structural arrangements for a calcium-binding site are discussed.

Binding Sites↗
PubMed1995

Structural consequences of ammonia binding to the manganese center of the photosynthetic oxygen-evolving complex: an X-ray absorption spectroscopy study of isotropic and oriented photosystem II particles.

The structure and orientation of the manganese complex in NH3-treated photosystem II (PS II) membrane particles of spinach are being studied by X-ray absorption spectroscopy. On the basis of earlier work by our group, a structure for the tetranuclear manganese complex of PS II, which consists of two di-mu-oxo-bridged binuclear Mn units linked by a mono-mu-oxo group, has been proposed [Yachandra, V. K., et al. (1993) Science 260, 675-679]. The extended X-ray absorption fine structure (EXAFS) of the complex modified by NH3 binding in the S2-state is suggestive of an increase in the Mn-Mn distance of one of these units from 2.72 +/- 0.02 to 2.87 +/- 0.02 A, whereas the Mn-Mn distance of the second unit seems to be unaffected by NH3 treatment. The elongation of one binuclear center could result from the replacement of one bridging mu-oxo by an amido group. The lengthening of one Mn-Mn distance means that, by NH3 treatment, the distance degeneracy of the 2.7 A Mn-Mn EXAFS interaction is removed. Consequently, the orientation of individual binuclear units with respect to the membrane normal becomes resolvable by EXAFS spectroscopy of partially oriented PS II membrane particles. The angle between the normal of the PS II-containing membrane and the Mn-Mn vector is determined to be 67 degrees +/- 3 degrees for the 2.87 A distance and 55 degrees +/- 4 degrees for the 2.72 A distance. Only small effects on position, shape, and orientation dependence of Mn K-edge spectra result from NH3 treatment, indicating that the Mn oxidation state, the symmetry of the Mn ligand environment, and the orientation of the complex remain essentially unaffected in the annealed NH3 S2-state. Therefore, it seems likely that the angles determined for the ammonia-modified manganese complex are similar to the respective angles of the untreated complex. The structure of the manganese complex and its orientation in the membrane are discussed.

Ammonia↗
PubMed1994

Orientation of the oxygen-evolving manganese complex in a photosystem II membrane preparation: an X-ray absorption spectroscopy study.

X-ray absorption spectroscopy has been performed on oriented photosystem II membrane particles isolated from spinach. Structural features of the tetranuclear Mn cluster and the orientation of the cluster with respect to the lipid bilayer were determined in both the S1 and S2 states of the Kok cycle. Variation of the sample orientation with respect to the X-ray e-vector yields highly dichroic K-edge and extended X-ray absorption fine structure spectra (EXAFS), indicative of an asymmetric tetranuclear cluster. Mn-Mn vectors at 2.72 and 3.38 A can be resolved from these measurements using quantitative analysis. The 2.72-A vector, consisting of at least two component vectors, is oriented at an average angle of 60 degrees +/- 7 degrees to the membrane normal, with an average of 1.1 +/- 0.1 interactions per Mn atom. The 3.38-A vector, most probably an average of two vectors, makes an angle of 43 degrees +/- 10 degrees with respect to the membrane normal, with an average of 0.45 +/- 0.07 backscatterer per Mn atom. Upon advance to the S2 state, the orientation of these vectors and the average numbers of backscatterers are approximately invariant. Analysis of more subtle features of the EXAFS reveals changes accompanying this S-state advance that are consistent with the oxidation of Mn during this transition. However, the dominant structural features of the oxygen-evolving complex remain constant in the S1 and S2 states. The structure of the Mn complex and the orientation of the complex in the membrane within the context of dichroism of the X-ray absorption data are discussed.

Chloroplasts↗
PubMed1994

Correlation between structure and magnetic spin state of the manganese cluster in the oxygen-evolving complex of photosystem II in the S2 state: determination by X-ray absorption spectroscopy.

The structure of the manganese cluster in the S2 state with the g approximately 4 EPR signal (S2-g4 state) generated by 130 K illumination of photosystem II (PSII) membranes prepared from spinach has been investigated by X-ray absorption spectroscopy. The Mn X-ray absorption K-edge spectra of the S2-g4 state not only show a shift of the inflection point to higher energy from the S1 state but also reveal a different edge shape from that of the S2 state with the multiline signal (S2-MLS state). Extended X-ray absorption fine structure (EXAFS) studies of the Mn K-edge show that the structure of the Mn cluster in the S2-g4 state is distinctly different from those in the S2-MLS or S1 states. In the S2-g4 state, the second shell of back-scatters from the Mn absorber is found to contain two Mn-Mn distances of 2.73 and 2.85 A. We interpret this to indicate the presence of two nonequivalent di-mu-oxo-bridged Mn binuclear structures in the Mn cluster of the S2-g4 state. The third shell of the S2-g4 state at about 3.3 A also contains increased heterogeneity. By contrast, very little distance disorder was found to exist in the second shell of the S1 or S2-MLS states. A mechanism is proposed to explain these results in the context of our model for the Mn cluster and the EPR properties of the Mn complex in the S2 state.

Electron Spin Resonance Spectroscopy↗
PubMed1993

ENDOR and ESEEM studies of cytochrome c oxidase: evidence for exchangeable protons at the CuA site.

Electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) spectroscopies were used to study whether protons in the immediate protein environment around CuA in cytochrome c oxidase are susceptible to solvent exchange. The enzyme was incubated in buffered D2O under resting or turnover conditions for 90 min and then frozen to quench the hydrogen/deuterium-exchange process. ENDOR spectra of the deuterated sample were essentially identical to those of control samples. The ESEEM spectra, however, provided a clear indication of the introduction of deuterium into the CuA environment following incubation in buffered D2O. The extent of deuterium incorporation was not affected by enzyme turnover. An analysis of the ESEEM data indicated that water is in reasonably close proximity to the CuA site, but not in the immediate coordination sphere of the metal(s). We estimate a minimum distance of 5.4 A between the CuA center and the protein/water interface. This relatively short surface separation distance is consistent with the role of CuA as the immediate oxidant of cytochrome c in the cytochrome oxidase (Hill, B. C. (1991) J. Biol. Chem. 266, 2219-2226).

Binding Sites↗
PubMed1993

Where plants make oxygen: a structural model for the photosynthetic oxygen-evolving manganese cluster.

In the photosynthetic evolution of oxygen, water oxidation occurs at a catalytic site that includes four manganese atoms together with the essential cofactors, the calcium and chlorine ions. A structural model and a determination of the manganese oxidation states based on x-ray absorption spectroscopy are presented. The salient features, in both higher plants and cyanobacteria, are a pair of di-mu-oxo bridged manganese binuclear clusters linked by a mono-mu-oxo bridge, one proximal calcium atom, and one halide. In dark-adapted samples, manganese occurs in oxidation states (III) and (IV). Data from oriented membranes display distinct dichroism, precluding highly symmetrical structures for the manganese complex.

Bridged-Ring Compounds↗
PubMed1992

The g = 2 multiline EPR signal of the S2 state of the photosynthetic oxygen-evolving complex originates from a ground spin state.

The amplitude of the g = 2 Mn 'multiline' EPR signal of the S2 state of the photosynthetic oxygen-evolving complex varies inversely with temperature, indicating that this signal arises from a ground spin state. Electron spin echo experiments at temperatures of 4.2 K and 1.4 K show such Curie-law behavior of the g = 2 multiline EPR signal, as do continuous-wave EPR experiments performed at a non-saturating microwave power in the range from 15.0 K to 4.2 K.

Electron Spin Resonance Spectroscopy↗
PubMed1992

The manganese site of the photosynthetic oxygen-evolving complex probed by EPR spectroscopy of oriented photosystem II membranes: the g = 4 and g = 2 multiline signals.

The g = 4 and g = 2 multiline EPR signals arising from the Mn cluster of the photosynthetic oxygen-evolving complex (OEC) in the S2 state were studied in preparations of oriented photosystem II (PSII) membranes. The ammonia-modified forms of these two signals were also examined. The g = 4 signal obtained in oriented PSII membranes treated with NH4Cl at pH 7.5 displays at least 16 partially resolved Mn hyperfine transitions with a regular spacing of 36 G [Kim, D.H., Britt, R.D., Klein, M.P., & Sauer, K. (1990) J. Am. Chem. Soc. 112, 9389-9391]. The observation of this g = 4 "multiline signal" provides strong spectral evidence for a tetranuclear Mn origin for the g = 4 signal and is strongly suggestive of a model in which different spin state configurations of a single exchange-coupled Mn cluster give rise to the g = 4 and g = 2 multiline signals. A simulation shows the observed spectrum to be consistent with an S = 3/2 or S = 5/2 state of a tetranuclear Mn complex. The resolution of hyperfine structure on the NH3-modified g = 4 signal is strongly dependent on sample orientation, with no resolved hyperfine structure when the membrane normal is oriented perpendicular to the applied magnetic field. The dramatic NH3-induced changes in the g = 4 signal resolved in the spectra of oriented samples are suggestive that NH3 binding at the Cl- site of the OEC may represent direct coordination of NH3 to the Mn cluster.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Membrane↗
PubMed1992

Torsional rigidity of positively and negatively supercoiled DNA.

Time-correlated single-photon counting of intercalated ethidium bromide was used to measure the torsion constants of positively supercoiled, relaxed, and negatively supercoiled pBR322 DNA, which range in superhelix density from +0.042 to -0.123. DNA behaves as coupled, nonlinear torsional pendulums under superhelical stress, and the anharmonic term in the Hamiltonian is approximately 15 percent for root-mean-square fluctuations in twist at room temperature. At the level of secondary structure, positively supercoiled DNA is significantly more flexible than negatively supercoiled DNA. These results exclude certain models that account for differential binding affinity of proteins to positively and negatively supercoiled DNA.

DNA, Superhelical↗