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Biomedical subjects

B Hedman

Publications and source records attributed to B Hedman.

31 records · Page 2Linked to original sources
PubMed1992

On the structure of the nickel/iron/sulfur center of the carbon monoxide dehydrogenase from Rhodospirillum rubrum: an x-ray absorption spectroscopy study.

The nickel/iron/sulfur center of the carbon monoxide dehydrogenase (carbon monoxide:(acceptor)oxidoreductase; EC 1.2.99.2) enzyme from Rhodospirillum rubrum (Rr-CODH) was studied by x-ray absorption spectroscopy at the Ni K edge. Extended x-ray absorption fine structure data show that the first Ni coordination shell consists of 2 S atoms at 2.23 A and 2-3 N/O atoms at 1.87 A. The edge structure indicates a distorted tetrahedral or five-coordinate Ni environment in both oxidized and reduced Rr-CODH. By comparing second-shell extended x-ray absorption fine structure data of Rr-CODH to that of (Et4N)3[NiFe3S4(SEt)4], a cubane-type cluster, it was clearly established that Ni in the Rr-CODH center is not involved in the core of a NiFe3S4 cubane cluster. One model consistent with the results is a mononuclear Ni2+ site, bridged by S-Cys or sulfide to one or both of the Fe4S4 clusters of the enzyme, with the remaining coordination sites occupied by additional S-Cys or N/O-liganding amino acid residues.

Absorptiometry, Photon↗
PubMed1989

Cyanide and methylisocyanide binding to the isolated iron-molybdenum cofactor of nitrogenase.

19F NMR and x-ray absorption experiments have been performed with both the isolated FeMo cofactor and the MoFe protein of nitrogenase in search of direct evidence for substrate or inhibitor binding. Using 19F NMR as a probe and p-CF3C6H4S- as the receptor ligand, the data show that the nitrogenase inhibitors CN- and CH3NC bind to the isolated FeMo cofactor-RFS- complex in N-methylformamide with a finite formation constant. Their binding increases the electronic relaxation time of the complex and increases the life-time of the FeMo cofactor-p-CF3C6H4S- bond, Parallel molybdenum K edge and extended x-ray absorption fine structure experiments show that CH3NC does not bind to molybdenum. Although CO and N3- both relieve CN- and CH3NC inhibition of electron flow through nitrogenase, unlike the latter, they do not appear to bind to isolated FeMo cofactor. In experiments with the dithionite-reduced MoFe protein, we did not detect any changes in the molybdenum K edge or extended x-ray absorption fine structure spectra upon addition of CO, N2, C2H2, NaCN, CH3NC, or azide demonstrating that either these substrates and inhibitors do not bind to molybdenum or that the FeMo cofactor site of nitrogenase is inaccessible to substrate binding except under turnover conditions.

Azotobacter↗
PubMed1988

Phase determination by multiple-wavelength x-ray diffraction: crystal structure of a basic "blue" copper protein from cucumbers.

A novel x-ray diffraction technique, multiple-wavelength anomalous dispersion (MAD) phasing, has been applied to the de novo determination of an unknown protein structure, that of the "blue" copper protein isolated from cucumber seedlings. This method makes use of crystallographic phases determined from measurements made at several wavelengths and has recently been made technically feasible through the use of intense, polychromatic synchrotron radiation together with accurate data collection from multiwire electronic area detectors. In contrast with all of the conventional methods of solving protein structures, which require either multiple isomorphous derivatives or coordinates of a similar structure for molecular replacement, this technique allows direct solution of the classical "phase problem" in x-ray crystallography. MAD phase assignment should be particularly useful for determining structures of small to medium-sized metalloproteins for which isomorphous derivatives are difficult or impossible to make. The structure of this particular protein provides new insights into the spectroscopic and redox properties of blue copper proteins, an important class of metalloproteins widely distributed in nature.

Amino Acid Sequence↗
PubMed1988

Women's health and women's work in health services: what statistics tell us.

This article draws together statistical information in several broad areas that relate to women's health, women's reproductive activities and women's occupations in Sweden. The statistical analysis reflects the major changes that have occurred in Swedish society and that have had a major impact on the health and well-being, as well as on the social participation rate, of women. Much of the data is drawn from a recent special effort at Statistic Sweden aimed at influencing the classification, collection and presentation of statistical data in all fields in such a way that family, working, education, health and other conditions of women can be more readily and equitably compared with those of men. In addition, social changes have seen the shifting of the responsibility of health care from the unpaid duties of women in the home to health care institutions, where female employees predominate. These trends are also discussed.

Adolescent↗
PubMed1987

A large reservoir of sulfate and sulfonate resides within plasma cells from Ascidia ceratodes, revealed by X-ray absorption near-edge structure spectroscopy.

The study of sulfur within the plasma cells of Ascidia ceratodes [Carlson, R. M. K. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 2217-2221; Frank, P., Carlson, R. M. K., & Hodgson, K. O. (1986) Inorg. Chem. 25, 470-478; Hedman, B., Frank, P., Penner-Hahn, J. E., Roe, A. L., Hodgson, K. O., Carlson, R. M. K., Brown, G., Cerino, J., Hettel, R., Troxel, T., Winick, H., & Yang, J. (1986) Nucl. Instrum. Methods Phys. Res., Sect. A 246, 797-800] has been extended with X-ray absorption near-edge structure (XANES) spectroscopy. An intense absorption feature at 2482.4 eV and a second feature at 2473.7 eV indicate a large endogenous sulfate concentration, as well as smaller though significant amounts of thiol or thioether sulfur, respectively. A strong shoulder was observed at 2481.7 eV on the low-energy side of the sulfate absorption edge, deriving from a novel type of sulfur having a slightly lower oxidation state than sulfate sulfur. The line width of the primary transition on the sulfur edge of a vanadium (III) sulfate solution was found to be broadened relative to that of sodium sulfate, possibly deriving from the formation of the VSO4+ complex ion [Britton, H. T. S., & Welford, G. (1940) J. Chem. Soc., 761-764; Duffy, J. A., & Macdonald, W. J. D. (1970) J. Chem. Soc., 977-980; Kimura, T., Morinaga, M., & Nakano, J. (1972) Nippon Kagaku Zaishi, 664-667]. Similar broadening appears to characterize the oxidized sulfur types in vanadocytes. A very good linear correlation between oxidation state and peak position (in electronvolts) was found for a series of related sulfur compounds. This correlation was used to determine a 5+ oxidation state for the additional sulfur type at 2481.7 eV. (ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Elicitation of thiomolybdates from the iron-molybdenum cofactor of nitrogenase. Comparison with synthetic Fe-Mo-S complexes.

Aerial oxidation of the iron-molybdenum cofactor (FeMoco) of Azotobacter vinelandii nitrogenase has been shown to yield either the tetrathiomolybdate ion ([MoS4]2-) or the oxotrithiomolybdate ion ([MoOS3]2-), depending on the reaction conditions. Thus, when N-methylformamide (NMF) solutions of FeMoco either were titrated with measured aliquots of air or were diluted with air-saturated NMF, [MoOS3]2- was found to be the predominant product while dilution of NMF solutions of FeMoco with air-saturated methanol produced [MoS4]2- almost exclusively. Similar aerial oxidation of solutions of chemically synthesized Fe-Mo-S clusters showed that significant information about the molybdenum environment in these species could be deduced from the nature of the elicited thiomolybdates. The differences in decomposition products as a function of solvent are postulated to be due to the loss through precipitation of the reducing agent sodium dithionite on addition of methanol but not NMF. These overall decomposition results are discussed in the context of recent X-ray absorption spectroscopic data which suggest the presence of an 'MoS3' core in FeMoco. A possible mechanism whereby [MoS4]2- might be rapidly formed from this core is presented.

Azotobacter↗
PubMed1985

Protein microcrystal diffraction and the effects of radiation damage with ultra-high-flux synchrotron radiation.

By using ultra-high-flux synchrotron x-radiation from a wiggler source, good Laue diffraction data have been obtained from protein microcrystals of size 30 X 35 X 10 microns3, mounted wet in glass capillaries. At the flux level of 10(13)-10(14) photons per sec/mm2, the radiation damage is still low enough to allow a large survey of reciprocal space for a microcrystal and a complete survey for a normal-sized protein crystal. The development of sources for ultra-high-intensity synchrotron radiation is thus an important improvement in the technique for determination of structure through protein crystallography as well as in other cases where crystal size is often a limiting factor.

Gramicidin↗
PubMed1984

On the spectral features associated with peroxide reactivity of the coupled binuclear copper active site in type 2 depleted and native Rhus laccase.

We report herein an X-ray absorption spectroscopic (XAS) determination of the oxidation state of the copper sites in T2D and native Rhus laccase. The increase in intensity of the 330 nm absorption feature which results from peroxide titration of T2D laccase (T3: [Cu(I)Cu(I)], T1: [Cu(II)]) is found to correlate linearly with the percent of oxidation of the binuclear copper site (determined by XAS analysis). This indicates that peroxide oxidizes but does not bind to the T3 site. We have used this correlation to determine that native laccase, as isolated, contains approximately 25% reduced T3 sites and that all spectral changes observed upon peroxide addition to native laccase can be accounted for by oxidation of these reduced sites. The importance of this result to previous reports of peroxide binding at the laccase active site is discussed.

Binding Sites↗
PubMed1981

Firing properties of single human motor units on maintained maximal voluntary effort.

The discharge properties on maintained maximal voluntary effort, axonal conduction velocity (a.c.v.) and contraction time (c.t.) of single human motor units were studied. Electromyographic (EMG) techniques were used and sufficient selectivity was obtained after repeated lesions to the terminal nerve twigs and consequent collateral sprouting, or by blocking the main muscle nerve in subjects with an accessory nerve supplying just one or a few units, or using high impedance wire electrodes. Most units with a.c.v. above 45 m/s and c.t. below 50 ms had maximal voluntary firing rates of about 50 Hz. On prolonged maximal effort, however, their rates rapidly decreased and after some seconds to a minute they ceased to respond tonically. As long as their motoneurons fired their EMG potentials were mainly intact and their twitch tension was significant. Most units with a.c.v. below 40 m/s and c.t. above 60 ms fired initially at 30 Hz, decreased slowly in firing rate and continued at 20 Hz for some minutes. We conclude that there is a central fatigue of units with short c.t. and high a.c.v. which protects their peripheral regions from severe exhaustion, but that there is no significant central fatigue of units with long c.t. and low a.c.v. We emphasize, however, that most units are intermediate in their properties.

Action Potentials↗
PubMed1981

The fatigue and voluntary discharge properties of single motor units in man.

1. The discharge properties of single motor units during prolonged maximal voluntary effort have been studied using electromyographic recordings, mainly in the short big toe extensor muscle but also in the anterior tibial muscle.2. The required selectivity of the e.m.g. recordings was achieved in the short big toe extensor muscle after previous mechanical lesions to the terminal nerve twigs and muscle fibres and consequent collateral sprouting, and in the anterior tibial muscle with the use of a high impedance wire electrode.3. During the first few hundred milliseconds of sustained maximal effort the motor units fired at rates ranging from about 30-60 Hz, and the tension was the same as that obtained on electrical tetanization of the nerve to the toe extensor muscles above 50 Hz.4. During prolonged maximal effort the firing rates and the proportion of motor units firing successively decreased. Motor units initially firing at 30 Hz continued to fire tonically but at 15-20 Hz. Motor units initially firing at 60 Hz ceased to fire tonically but could still be made to discharge phasically. The period of time during which all motor units responded tonically could be increased from some seconds up to 20 sec by long-term training.5. Motor units with a limited endurance fired at a lower tension in the early than in the late stages of maintained contraction.6. It is suggested that motoneurones innervating slow twitch muscle fibres respond continuously to prolonged voluntary drive at rates sufficient for full fusion but that the threshold of motoneurones innervating fast twitch muscle fibres increases so that they finally mainly fire phasically thus protecting the peripheral excitation and contractile mechanisms from excessive exhaustion.

Action Potentials↗
PubMed1979

Contraction time and voluntary discharge properties of individual short toe extensor motor units in man.

1. The contraction time and the voluntary discharge properties of forty-five short toe extensor motor units were studied in man. 2. The contraction time of the individual motor unit was studied by using selective electrical nerve stimulation or by averaging the increase in force related to its electromyographic potential in tonic voluntary contraction. 3. Both methods showed a range of contraction times from 40 to 90 ms. 4. The discharge properties of the individual motor unit were studied with e.m.g. techniques, permitting the identification of its potentials during maximum voluntary effort. 5. A motor unit which could be driven continously and had a minimum rate of about 10/s and a maximum rate of about 30/s had a contraction time between 60 and 90 ms. 6. A motor unit which could not be driven continously and had a minimum rate of about 20/s and a maximum rate above 40/s had a contraction time between 40 and 55 ms. 7. A motor unit with intermediate voluntary discharge properties had an intermediate contraction time. 8. It is concluded that each motor unit fires at its fusion frequency in voluntary contraction and that the voluntary discharge frequency range of a motor unit can be used as an indication of its contraction time.

Action Potentials↗