The ferritins: molecular properties, iron storage function and cellular regulation☆

Oxide pyrochlores — A review

The density of states on a fractal is calculated taking into account the scaling properties of both the volume and the connectivity. We use a Green's function method developed elsewhere which utilizes a relationship to the diffusion problem. It is found that proper mode counting requires a reciprocal space with new intrinsic fracton dimensionality d = 2 d/(2 + δ). Here, d is the effective dimensionality, and δ the exponent giving the dependence of the diffusion constant on distance. For example, we find for percolation clusters d = 4/3 within the numerical accuracy available, independent of the Euclidean dimensionality d. Crossover to normal behaviour at low frequencies is discussed for finite fractals and for percolation above the percolation threshold pc. Relevance to experimental results on proteins is also discussed.

/pdf/density-of-states-on-fractals-fractons-1r1wxh276y.pdf

Density of states on fractals : « fractons »

A survey is given of the physical properties, composition and crystal structure of intermetallic compounds formed between rare-earth elements and 3d transition elements. Apart from binary compounds the results of pseudobinary series are also considered. The magnetic properties determined by the exchange interactions involving 4f as well as 3d electrons, are discussed together with experimental results available on magnetovolume effects and various resonance techniques such as NMR and the Mossbauer effect.

https://iopscience.iop.org/article/10.1088/0034-4885/40/10/002/pdf

Intermetallic compounds of rare-earth and 3d transition metals

Structural fluctuations in proteins on the picosecond timescale have been studied in considerable detail by theoretical methods such as molecular dynamics simulation1,2, but there exist very few experimental data with which to test the conclusions. We have used the technique of inelastic neutron scattering to investigate atomic motion in hydrated myoglobin over the temperature range 4–350 K and on the molecular dynamics timescale 0.1–100 ps. At temperatures below 180 K myglobin behaves as a harmonic solid, with essentially only vibrational motion. Above 180 K there is a striking dynamic transition arising from the excitation of non-vibrational motion, which we interpret as corresponding to tor-sional jumps between states of different energy, with a mean energy asymmetry of KJ mol −1. This extra mobility is reflected in a strong temperature dependence of the mean-square atomic displacements, a phenomenon previously observed specifically for the heme iron by Mossbauer spectroscopy3–5, but on a much slower timescale (10−7 s). It also correlates with a glass-like transition in the hydration shell of myoglobin6 and with the temperature-dependence of ligand-binding rates at the heme iron, as monitored by flash photolysis7. In contrast, the crystal structure of myoglobin determined down to 80 K shows no significant structural transition8–10. The dynamical behaviour we find for myoglobin (and other globular proteins) suggests a coupling of fast local motions to slower collective motions, which is a characteristic feature of other dense glass-forming systems.

Dynamical transition of myoglobin revealed by inelastic neutron scattering.

Bacterioferritin isolated from Escherichia coli is of two kinds: a protein containing a polynuclear iron compound, the bacterioferritin proper and a protein free of the polynuclear iron compound, the apo-bacterioferritin. Bacterioferritin of both kinds is characterized by absorption maxima at 417,530 and 560 nm, contributed by protohaem IX. Single crystals of bacterioferritin of the space group I432 suggest that the molecule is made up of 24 identical subunits related by a cubic point symmetry. The molecular weight of the protein subunit, as determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, is 15000. In the electron microscope the bacterioferritin molecule appears to be a sphere of 9.5 nm (95 A) diameter composed of a negatively staining outer shell and an inner electron-dense core of 6 nm (60 A) diameter.

The composition and the structure of bacterioferritin of Escherichia coli.

The 57Fe gamma-ray resonance absorption spectra have been measured in crystals of metmyoglobin and deoxymyoglobin over a wide range of temperatures. Above a critical temperature common to both proteins (220 K), the dynamics of heme iron display a dramatic change, in that two kinds of thermal fluctuations come into play--a fast fluctuation associated with a steep decrease of the total fluctuation of characteristic time 10(-8) sec, associated with bounded diffusive motion. By using both discrete jump and continuous diffusion models, the latter based on the Brownian motion of an overdamped harmonic oscillator, the essential parameters of the iron motion (mean square displacement and jump frequency or diffusion constant) can be derived as a function of temperature. Thus, for deoxy Mb at 288 K, the mean square displacement for the fast fluctuation is about 6 X 10(-2) A2 and for the diffusive motion is 1.6 X 10(-2) A2; the diffusion constant is 4 X 10(-10) cm2/sec. The diffusive process is associated with an activation energy of about 0.75 kcal/mol. Although the same general kinds of phenomena are observed in crystals of MetMb and deoxy Mb, significant differences in behavior are found, which suggest that the main dynamical phenomenon observed reflects internal large-scale motions of the protein.

https://www.pnas.org/content/pnas/80/3/736.full.pdf

Dynamics of heme iron in crystals of metmyoglobin and deoxymyoglobin.

Mössbauer Absorption in Overdamped Harmonically Bound Particles in Brownian Motion

M\"ossbauer studies of the 86-keV transition of ${\mathrm{Gd}}^{155}$ in ${\mathrm{Gd}}_{1\ensuremath{-}x}{R}_{x}$ compounds yield the hyperfine interaction parameters as a function of lattice dimensions and the angle $\ensuremath{\theta}$ between the magnetization and the $c$ axis. The magnetic hyperfine field is anisotropic, $\frac{{H}_{\mathrm{eff}}(\ensuremath{\theta}=28\ifmmode^\circ\else\textdegree\fi{})}{{H}_{\mathrm{eff}}(\ensuremath{\theta}=47\ifmmode^\circ\else\textdegree\fi{})}=1.13$. The ratios between the electric field gradients in various metallic crystals are in agreement with the point-charge model. The absolute values of the gradients are about twice the theoretical values.

Anisotropic hyperfine interactions in gadolinium metal

The recoilless-absorption spectra of the 21.6-keV $\ensuremath{\gamma}$ rays of ${\mathrm{Eu}}^{151}$ in ${\mathrm{Eu}}_{x}{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{2}$ are composed of a few lines which exhibit strongly temperature-dependent isomer shifts. The results are interpreted in terms of fast fluctuations of electrons between a localized $4f$ level and the conduction band. The energy released by removing an electron from the $4f$ level to the conduction band (0.01-0.1 eV) depends significantly on the number of La nearest neighbors. The levels have a width of \ensuremath{\sim} 0.01 eV.

Charge fluctuations and local-environment dependence of the energy of the 4f virtual localized level of Eu in Eu/sub x/ La/sub 1-x/ Rh$sub 2$

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