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P Eisenberger

Publications and source records attributed to P Eisenberger.

At least 19 recordsLinked to original sources
PubMed1983

X-ray diffraction by phospholipid monolayers on single-crystal silicon substrates.

Monolayers of dipalmitoyl phosphatidylcholine have been transferred from an air-water interface to single-crystal silicon wafers previously alkylated with octadecyltrichlorosilane. By using synchrotron radiation it has been found possible to observe diffraction by single-crystal regions of these monolayers with negligible background scattering from the solid substrate. In one series of experiments, diffraction signals at Bragg spacings of 0.4247 +/- 0.0002 nm and 0.4253 +/- 0.0002 nm were observed. The supported phospholipid monolayer crystals show remarkably high in-plane order: the positional coherence length is at least 500 nm and the orientational order is better than 0.01 degrees . Preliminary temperature scans were carried out. The data reveal the existence of a phase transition at about 65 degrees C.

Journal Article↗
PubMed1982

The location of redox centers in biological membranes determined by resonance x-ray diffraction. I. Observation of the resonance effect.

We have developed resonance X-ray diffraction methods to locate for the first time intrinsic metal atoms associated with redox centers within biological membrane systems. The study of membranes containing dilute concentrations of resonant scatterers has been made possible by the development of synchrotron radiation sources of X-rays. The technique permits altering the scattering power of a particular atom relative to others by varying the incident X-ray energy. Thus, this method may be used to locate a metal atom within a complex integral protein without chemical modification of the membrane. We present resonance diffraction data taken with synchroton radiation for two different membrane systems: cytochrome oxidase incorporated into lipid vesicles and a photosynthetic reaction center-cytochrome c complex also reincorporated into lipid vesicles.

Cell Membrane↗
PubMed1982

The location of redox centers in biological membranes determined by resonance x-ray diffraction. II. Analysis of the resonance diffraction data.

In the preceding paper (Stamatoff, J., Eisenberger, P., Blasie, J.K., Pachence, J.M., Tavormina, A., Erecinska, M., Dutton P.L. and Brown, G. (1982) Biochim. Biophys. Acta 679, 177-187), we described the observation of resonance X-ray scattering effects from intrinsic metal atoms associated with redox centers in membrane proteins on the lamellar X-ray diffraction from oriented multilayers of reconstituted membranes. In this paper, we discuss the possible methods of analysis of such data and present the results of our model refinement analysis concerning (a) the location of the cytochrome c heme iron atom in the profile structure of a reconstituted membrane containing a photosynthetic reaction center-cytochrome c complex and (b) the location of the heme a and a3 iron atoms in the profile structure of a reconstituted membrane containing cytochrome oxidase. The former results are of special importance because they provide a test of the validity of the resonance diffraction data and the methods of analysis, since the location of cytochrome c in the reaction center-cytochrome c membrane profile is known independently of the resonance diffraction experiments.

Animals↗
PubMed1982

The electronic structure of Fe2+ in reaction centers from Rhodopseudomonas sphaeroides. II. Extended x-ray fine structure studies.

Extended x-ray absorption fine structure (EXAFS) studies were performed on reaction centers (RC) of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26. RC containing two, one, and no quinones (2Q, 1Q, 0Q) samples were studied. The average ligand distance of the first coordination shell was determined to be 2.10 +/- 0.02 A with a more distant shell at 4.14 +/- 0.05 A. The Fe2+ site in RC was found to have a very large structural disorder parameter, from which a spread in ligand distance per iron site of approximately +/- 0.1 A was deduced. The most likely coordination number of the first shell is six, with a mixture of oxygens and nitrogens as ligands. The edge absorption results are consistent with the Fe2+ being in distorted octahedral environment. The EXAFS spectra of the 2Q and 1Q samples with and without O-phenanthroline were found to be the same. This indicates that either the secondary quinone and o-phenanthroline do not bind to Fe2+ or that they replace an equivalent ligand. The 0Q sample showed a 12% decrease in the EXAFS amplitude, which was restored upon addition of o-phenanthroline. These results can be explained by either a loss of a ligand or a severe conformational change when the primary quinone was removed.

Chemical Phenomena↗
PubMed1979

X-ray scattering from labeled membranes.

We present a new method for the determination of structural parameters in biological membranes. Recording the continuous scattering of heavy-atom labeled membranes and applying elementary Fourier methods we obtain the scattering of the heavy-atom distribution alone. The details of this distribution are explored by developing a simple model and testing for cases relevant to biological membranes. We find that the intensity distribution is highly sensitive to many key parameters. The increased signal from heavy-atom labeling and the use of an improved x-ray system make it possible to record patterns from dilute membrane suspensions. Thus determination of these parameters is possible in the same environment where many membrane biochemical studies are performed. Application of the method is made to a model lipid bilayer membrane, dipalmitoyl phosphatidylcholine by labeling with UO2++ ions. We determine the precise distance between UO2++ layers on either side of the membrane as well as the width of the label on each side. This determination permits estimation of phosphate separation across single labeled bilayers in an aqueous suspension.

Lipid Bilayers↗
PubMed1978

Extended X-ray absorption fine structure determination of iron nitrogen distances in haemoglobin.

EXAFS spectra have been obtained of oxy and deoxy complexes of haemoglobin and of the 'picket fence' porphyrin, using synchrotron radiation as a source of X rays. The fluorescence data were Fourier filtered to obtain distances to the first shell and corrections applied to remove contributions from the axial ligands. In this way, the iron to porphinato nitrogen distances were determined to be 1.98 +/- 0.01 A for both oxygenated complexes and 2.055 +/- 0.01 A for both deoxy forms.

Hemoglobins↗
PubMed1978

EXAFS: new horizons in structure determinations.

Although the phenomena of extended x=ray absorption fine structure (EXAFS) were observed as early as the 1930's, EXAFS has only recently, with the utilization of synchrotron radiation, been transformed into a powerful structural technique. The theory and experimental practice of the technique are described and illustrated with data on germanium. Applications to systems as diverse as hemoglobin, polymer-bound catalysts, ions in solution, amorphous solids, and adsorbate atoms on surfaces are reviewed. With the recent approval of funding for new, more powerful dedicated synchrotron sources, the future holds the possibility of a virtual revolution in structure determinations.

Chemical Phenomena↗
PubMed1978

Superoxide dismutase, a study of the electronic properties of the copper and zinc by X-ray absorption spectroscopy.

The x-ray absorption for copper and zinc in oxidized and reduced superoxide dismutase, as well as in various model compounds, was studied. Upon reduction of the protein, the added electron affects the copper site almost exclusively, while the zinc remains virtually unchanged. Reduction decreases the charge on the copper atom [toward Cu(I)] and changes the configuration of the copper site so that it becomes less symmetric. An analysis of the copper absorption observed with the oxidized enzyme and a comparison with that for Cu(II)(imid)4 suggests that the copper is not simply ligated to four imidazoles. The addition of H2O2 to superoxide dismutase reduces the copper to Cu(I), while oxygen addition to the peroxide-reduced protein restores the copper to Cu(II).

Absorption↗
PubMed1978

GLC determination of warfarin in human plasma.

A specific and quantitative GLC method for warfarin in human plasma is described. The procedure uses papaverine as the internal standard and involves a dichloroethane extraction of the acidified specimen. The organic extract is evaporated, and the evaporated extract is dissolved in 50 microliter of chloroform. Aliquots of 2-3 microliter are injected into a gas chromatograph equipped with a flame-ionization detector. The sensitivity of the method is such that 0.3 microgram of intact warfarin can be detected in 1 ml of plasma. Statistical analyses indicate a recovery of 97.26 +/- 1.89% SD. The procedure was successfully applied to plasma drug level studies in humans.

Adult↗
PubMed1976

Structure-function relations in hemoglobin as determined by x-ray absorption spectroscopy.

Conclusions concerning the structure around the iron atom in oxy- and carbonmonoxyhemoglobin have been obtained by fluorescent x-ray absorption studies. The bis-imidazole heme complex was used as a model system of known structure. The ligated forms of hemoglobin, and cytochrome c at high pH, gave spectra which were very similar to the bis-imidazole complex, where the average Fe-N bond distance is known to be 1.98 A. By comparison it was possible to determine that the average Fe-N bond distances were 1.99 A in oxyhemoglobin, 1.98 A in carbonmonoxyhemoglobin, and 1.98 A in cytochrome c at pH less than 10.5, with an experimental accuracy of +/-0.02 A. An experimental comparison between oxy- and deoxyhemoglobin A showed much larger spectral changes than amongst the ligated forms. A comparison was made between the low oxygen affinity form of deoxy HbA and the high affinity form of doexy Hb Kempsey (alpha2beta992 Asp leads to Asn). All the spectral features coincided, allowing us to conclude that the average iron-ligand bond differences must be less than or equal to 0.02 A. Since the strain energy is proportional to the square of this displacement, we show that the strain energy at the iron is less than or equal to 4 X 10(-3) eV. This is negligible compared to the difference of binding energy of the high and low affinity forms, which is 0.15 eV, showing that the energies responsible for the increase of oxygen affinity are not localized at the heme.

Carboxyhemoglobin↗